Rear steering control for a vehicle

ABSTRACT

A steering system and method for a vehicle having steerable front and rear wheels has rear hydraulic steering device that may be coupled to one or more of the rear wheels. A rear valve assembly may hydraulically control the rear hydraulic steering device to steer the rear wheels based upon a rear steering command from a controller. In a manual steering mode, the controller does not determine a rear steering command for the rear valve assembly such that the rear wheels are freely rotatable. In a rear steering assist mode, the controller determines the rear steering command based upon, at least in part, the manual steering input.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of application Ser. No. 15/183,475,filed Jun. 15, 2016, now allowed, which is a continuation of applicationSer. No. 14/455,708, filed Aug. 8, 2014, now U.S. Pat. No. 9,370,138.

STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE DISCLOSURE

This disclosure relates to the steering of vehicles, including vehicleswith caster-mounted rear wheels.

BACKGROUND OF THE DISCLOSURE

In various settings, relatively precise steering of vehicles may beimportant. For example, in agricultural settings it may be important toprecisely steer an agricultural work vehicle across a field in order toseed, tend, harvest, or otherwise process crops or other material.

In certain vehicles, the configuration of one set of wheels may varyfrom the configuration of another set of wheels. For example, in variouscombines, windrowers, or other vehicles, a rear set of wheels may bemounted on casters, whereas a forward set of wheels may be mounted to afixed axle (or axles). In certain embodiments, the forward wheels may befixed in a forward-facing orientation (i.e., may not be configured toturn to the sides to steer the vehicle). In such a configuration, thevehicle may be steered at the front wheels by driving the front wheelsat different speeds from each other. For example, a dedicated hydraulicmachine (e.g., a dedicated hydraulic pump) may be provided for each ofthe front wheels, such that each wheel may be driven independently ofthe other.

It may be useful to provide a system to control the steering of both thefront and the rear wheels of these types of vehicles, as well as thewheels of vehicles having various other configurations. Known steeringcontrol methods may include, for example, the use of a rack and pinionarrangement that is mechanically connected to a steering input device(e.g., a steering wheel), an Ackermann linkage, or another mechanicaldevice. As the steering input device is moved by an operator, this maymechanically rotate the pinion with respect to the rack, therebymechanically driving movement of the rack (or otherwise move therelevant mechanical device). The movement of the rack (or other device)may in turn, for example, control steering of a set of front wheels or aset of rear wheels. With regard to the rear wheels, for example, themechanical movement of the rack and pinion may mechanically port flow ofhydraulic fluid to hydraulic cylinders at the rear of the vehicle, inorder to control steering of a set of rear wheels.

SUMMARY OF THE DISCLOSURE

A steering system and method are disclosed for controlling the steeringof one or more steerable rear wheels (and other wheels) of a vehicle.

According to one aspect of the disclosure, a steering system for anagricultural vehicle has one or more steerable front wheels, one or moresteerable rear wheels, and a steering input device configured to receivea manual steering input for the one or more steerable front wheels. Thesteering system has a rear hydraulic steering device coupled to at leastone of the one or more steerable rear wheels. A rear valve assembly isconfigured to hydraulically control the rear hydraulic steering deviceto steer the at least one steerable rear wheel. A controller isconfigured to determine a rear steering command and provide the rearsteering command to the rear valve assembly. The rear valve assemblyhydraulically controls the rear hydraulic steering device based upon, atleast in part, the rear steering command from the controller. In amanual steering mode, the controller does not determine a rear steeringcommand for the rear valve assembly such that the rear wheels are freelyrotatable. In a rear steering assist mode, the controller determines therear steering command based upon, at least in part, the manual steeringinput.

According to another aspect of the disclosure, a steering method for anagricultural vehicle has one or more steerable front wheels, one or moresteerable rear wheels, a steering input device configured to receive amanual steering input for the one or more steerable front wheels, a rearhydraulic steering device coupled to at least one of the one or moresteerable rear wheels, a rear valve assembly configured to hydraulicallycontrol the rear hydraulic steering device in order to steer the atleast one steerable rear wheel, and a controller. The steering methodincludes determining, in at least one mode, a rear steering command by acontroller; providing, in at least one mode, the rear steering commandto the rear valve assembly; and hydraulically controlling, in at leastone mode, the rear hydraulic steering device with the rear valveassembly based upon, at least in part, the rear steering command fromthe controller. In a manual steering mode, the controller does notdetermine a rear steering command for the rear valve assembly such thatthe rear wheels are freely rotatable. In a rear steering assist mode,the rear steering command is determined based upon, at least in part,the manual steering input.

In certain embodiments, a steering sensor in communication with thesteering input device may provide a steering input signal based upon thesteering sensor detecting the manual steering input. In the rearsteering assist mode, the rear steering command may be determined basedupon the steering input signal. In the automated steering mode, the rearsteering command may be determined independently of manual steeringinput. The automated steering mode may be terminated based uponreceiving the manual steering input at the steering input device.

In certain embodiments, a front hydraulic steering device may be coupledto the front wheels. In the automated steering mode, a front valveassembly may control the front hydraulic steering device based upon thetarget path of the vehicle. In the rear steering assist mode, the fronthydraulic steering device may steer the front wheels based upon themanual steering input.

In certain embodiments, dual-path hydraulic systems may be utilized forsteering control. For example, a double-acting piston may be included inthe rear hydraulic steering device, such that steering of the rearwheels may be controlled by the rear valve assembly controllinghydraulic flow to the double-acting piston.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features and advantages willbecome apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified view of an example agricultural vehicle with rearcasters;

FIG. 2 is a schematic view of an example steering system for a vehiclewith rear casters;

FIG. 3 is a schematic view of another example steering system for avehicle with rear casters;

FIG. 4 is a schematic view of yet another example steering system for avehicle with rear casters;

FIG. 5 is a schematic view of an example hydraulic system included inthe example steering system of FIG. 4;

FIG. 6 is a diagrammatic view of a steering control method that may beimplemented with the hydraulic system of FIG. 5;

FIG. 7 is another diagrammatic view of the steering control method ofFIG. 6;

FIG. 8 is a diagrammatic view of a fault detection method that may beimplemented for the hydraulic system of FIG. 5;

FIG. 9 is a diagrammatic view of another steering control method thatmay be implemented with the hydraulic system of FIG. 5; and

FIG. 10 is a diagrammatic view of further aspects of the steeringcontrol method of FIG. 9.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

The following describes one or more example embodiments of the disclosedsteering systems (and methods), as shown in the accompanying figures ofthe drawings described briefly above. Various modifications to theexample embodiments may be contemplated by one of skill in the art.

As also noted above, known steering control systems may employ amechanical link as a main connector between a steering input device(e.g., a steering wheel) and a control system for the steering variouswheels of a vehicle. For example, a rack and pinion assembly orAckermann linkage may be utilized to tie a steering wheel to the wheelsof a vehicle, or to a steering device connected to the wheels. Use ofsuch a mechanical link, however, may impede various strategies forautomating (including partially automating) steering control. Forexample, in known combines, a mechanical link (e.g., a rack and pinionarrangement or Ackermann linkage) may be utilized to connect a steeringinput device (e.g., a steering wheel) to a steering control device(e.g., a control valve for a hydraulic pump or motor), such that anymanual steering input received at the steering input device is conveyedby the mechanical link to the steering control device. Accordingly, inorder to steer the vehicle, an operator may provide a manual steeringinput at the steering input device, thereby causing the mechanical linkto mechanically control the steering control device.

With such a configuration, however, in order to transition from manualsteering to automated (or partially automated) steering, various systemsor devices must be provided to circumvent (or ignore or otherwisedisable) any mechanical control being provided by the mechanical link.This may complicate (or otherwise impede) the automation of front andrear steering for a vehicle. In certain instances, for example, a motormay be provided that translates automated steering commands intomechanical movement of the steering input device, thereby, in essence,replacing the manual steering input at the steering input device with anautomated mechanical steering input at the steering input device. Thismay introduce significant complexity to the steering system, and theautomated movement of a steering input device may be problematic forcertain operators.

To address these issues and others, it may be useful to provide asteering system (and method) in which front and rear steering operationsare controlled, at least in part, with hydraulic valve assemblies andvarious hydraulic circuits. Further, it may be useful to provide asteering system in which the mechanical link between the steering inputdevice and a steering control device for the front or rear wheels of thevehicle has been eliminated. In this way, a more efficient and effectivetransition between automatic and non-automatic steering may be obtained.

In certain embodiments, a steering input device may be configured tooperate a hydraulic steering valve (e.g., a manual valve) based uponmanual steering input received at a steering input device. Hydraulicflow through the steering valve, as controlled by the manual steeringinput, may then be utilized to control steering of the vehicle bycontrolling various hydraulically operated steering devices (e.g.,various double-acting pistons) for one or more of the vehicle wheels(e.g., two front wheels and two rear wheels). Various hydraulic controlcircuits may also be provided, which may be configured to provideautomatic steering control signals to various of the steering devices.Because a non-mechanical (e.g., hydraulic) connection may be utilized tocommunicate the manual steering input from the steering input device tothe various steering control devices, it may be possible to relativelyeasily transition from manual steering to automatic steering byselectively utilizing the hydraulic control circuits, rather than thesteering input device, to control the various hydraulic steeringdevices.

In certain embodiments, two front wheels of a vehicle may be configuredto be independently rotated, respectively, by separate hydraulic motors(e.g., swash-plate piston motors). The motors, in turn, may be driven torotate, respectively, by separate hydraulic pumps. In order to controlthe speed of the hydraulic pumps, a manually-operated steering valve maybe configured to regulate hydraulic flow to either end of adouble-acting piston (and cylinder). Opposite ends of the piston may bein mechanical (or other) communication with the hydraulic pumps, suchthat the position of the piston controls the relative speeds of each ofthe pumps. In this way, a particular manual steering input may result ina particular flow through the manual steering valve. This flow maydispose the double-acting piston at a particular orientation and thepiston may thereby cause the hydraulic pumps (and, accordingly, thehydraulic motors and the front wheels) to operate at particular speeds.Notably, because the hydraulic motors for the front wheels may be drivenseparately by the separate hydraulic pumps, it may be possible to drivethe front wheels at different speeds (e.g., as based upon manualsteering input) and thereby steer the vehicle.

It may also be possible to steer the front wheels automatically, ratherthan based upon manual steering input. For example, an electronically(or otherwise) controlled front hydraulic valve assembly may also beplaced in communication with the double-acting piston for steering thefront wheels. Control signals (i.e., particular hydraulic flows andpressures) from this valve assembly may then be utilized, in place ofmanual steering input, to automatically steer the front wheels. Notably,in such a configuration, a vehicle may be transitioned from manualsteering to automated steering, by transitioning control of thedouble-acting piston from the manually-operated steering valve (asdiscussed above) to the automatically-operated front valve assembly. Forexample, the steering valve for manual steering input may be configuredsuch that when the steering input device is returned to a neutralposition (e.g., when a steering wheel re-centered) no hydraulic flow isrouted through the steering valve to the double-acting piston (e.g., thesteering valve may be a closed-center valve). Accordingly, duringautomated steering, the steering input device may be returned toneutral, such that hydraulic steering signals may be received at thesteering device from the front valve assembly, but not themanually-operated steering valve. Accordingly, the front steering may beautomatically controlled by the front valve assembly (and associatedelectronic controllers), rather than manually controlled by the steeringinput device.

In certain embodiments, in order to control the steering of the rear (orother) wheels, a sensor may be placed in communication with the steeringinput device. The sensor may be configured to sense manual steeringinput at the steering input device and to transmit a correspondingsteering input signal (e.g., directly, or indirectly, via a controller)to an electronically (or otherwise) controlled rear hydraulic valveassembly. In this way, the rear valve assembly may facilitate thesteering of the rear wheels based upon the manual steering input sensedby the steering sensor, without the need for a direct mechanical linkbetween the steering input device and the rear valve assembly (and anyassociated steering device). For example, a steering sensor may beconfigured to detect a rate of steering or a degree of steering at asteering wheel (or other steering input device) and transmit acorresponding signal to a controller. The controller may then provide asteering command to the rear valve assembly, based upon the steeringsignal from the sensor. Based upon the steering commands, the rear valveassembly may then control a hydraulically operated rear steering device(e.g., one or more additional double-acting pistons) in order toautomatically steer the rear wheels.

In certain embodiments, one or more rear wheels of a vehicle may be inmechanical communication with one or more double-acting pistons (orother steering control devices), such that actuation of the pistonscontrols steering of the rear wheels. In order to steer such a vehicle,an operator may turn a steering wheel by a particular amount (e.g., aparticular number of degrees) or at a particular rate (e.g., aparticular number of degrees per second), or otherwise provide a manualsteering input. A sensor in communication with the steering wheel maysense this steering input and transmit a corresponding electrical (orother) steering signal to a controller. The controller may interpret orotherwise process the steering signal in order to provide an appropriatecommand signal to various valves within a rear valve assembly.Accordingly, the hydraulic flow through these valves (and through therear valve assembly as a whole) may be regulated based upon the sensedmanual steering input. In turn, the flow through the rear valve assemblymay control the actuation of the double-acting piston (or anothersteering device) at each of the rear wheels of the vehicles. In thisway, the rear wheels may be automatically steered in accordance with themanual steering input at the steering wheel, without requiring a directmechanical link between the steering input device and the rear steeringdevices.

In certain embodiments, the front wheels may alternatively (oradditionally) be steered automatically, with the speed of rotation ofthe front wheels (or other parameters) being controlled independently ofany manual steering input at the relevant steering input device. Forexample, a front valve assembly (e.g., as also described above) may beconfigured to automatically activate a steering device for the frontwheels, based upon a target path for the vehicle rather than a manualsteering input at the steering input device. For example, a target path(e.g., a straight line extending across a field) may be determinedindependently of manual steering input (e.g., based upon a predeterminedharvesting plan for a field). The front valve assembly may be configuredto automatically move a double-acting piston to control the speed ofleft- and right-side drive pumps, based upon a target path of travel forthe vehicle. Accordingly, the vehicle may be automatically steered atthe front wheels based upon a target path of travel.

In certain embodiments, a Global Positioning System (“GPS”) device maybe utilized to compare a vehicle's current position (or projected pathof travel) with a target path of travel across a field (or otherterrain). Appropriate automatic steering commands (i.e., electricalcontrol signals) for the front valve assembly may be determined withrespect to the vehicle's current position and the target path of travel(e.g., may be determined by a controller, based upon calibratedparameters, a look-up table, or other factors). Based upon receivingthese steering commands, the front valve assembly may automaticallycontrol steering of the front wheels of the vehicle in order to causethe vehicle to follow the target path. For example, in order to keep avehicle moving along a target path of travel (e.g., as determined usinga GPS device), a controller may automatically regulate hydraulic flowthrough various valves within the front valve assembly in order toactuate a double-acting piston for the steering of the front wheels.

The rear wheels may also sometimes be steered based upon a target pathof travel for the vehicle. For example, when the front wheels are beingautomatically steered based upon GPS information (as described above),the rear wheels may also be automatically steered to improve thevehicle's tracking of the target path of travel. In certain embodiments,such automated rear steering may also be effected with double-actingpistons in communication with the various rear wheels (as also describedabove).

Among other benefits, the steering system (and method) described hereinmay allow for operation of a vehicle in multiple steering modes,including a manual steering mode (or “manual mode”), a manual mode withrear steering assist (i.e., a “rear steering assist mode”), and anautomated steering mode (or “automated mode”). In the manual mode, thesteering of the forward wheels may be controlled by an operator viamanual input to a steering input device such as a steering wheel. Asnoted above, for example, a manual steering input at a steering inputdevice may operate a manual valve to selectively port hydraulic fluid toeither side of a double-side piston (or otherwise actuate a differentsteering device) and thereby cause the front wheels to be rotated atdifferent speeds.

In the rear steering assist mode, the steering of the rear wheels may becontrolled automatically based upon the manual steering of the frontwheels, such that the rear wheels may supplement the manual steeringcontrol of the front wheels. (As such, it will be understood that avehicle may operate simultaneously in the manual steering and rearsteering assist modes.) In certain implementations, steering of thefront wheels may be directly controlled based upon manual steering inputat a steering input device, and steering of the rear wheels may becontrolled by automated steering commands that are determined based uponthe manual steering input. For example, a steering sensor may detect arate (or degree) of steering at a steering input device and providecorresponding steering signals to a controller. Based upon thesesteering signals, the controller may then regulate flow through a rearvalve assembly to control the rear steering based upon signals from thesteering sensor. The rear wheels may be automatically steered to turnthe rear of the vehicle in an opposite direction from themanually-steered front of the vehicle, in order to decrease theeffective turning radius of the vehicle for a given operation, or may beotherwise automatically steered to appropriately align the vehicles withthe desired path of travel indicated by the manual steering input.

In the automated mode, steering of the forward wheels and the rearwheels may be controlled automatically, without manual steering inputfrom an operator. For example, in order to direct a vehicle along atarget path of travel, a controller may automatically regulate hydraulicflow through a front valve assembly to automatically control steering ofthe front wheels, and the same (or a different) controller mayautomatically regulate hydraulic flow through a rear valve assembly toautomatically control steering of the rear wheels. In the automatedsteering mode, a target path of travel may be utilized to determinevarious steering commands. For example, GPS information may be utilizedto identify whether a vehicle is deviating (or is expected to deviate)from a target path of travel, and steering commands (e.g., variouscontrol signals for relevant valve assemblies) determined accordingly.

A steering system (and method), as described herein, may also facilitaterelatively easy customization of steering control by operators of avehicle. For example, where front and rear valve assemblies areconfigured to control, respectively, front and rear steering of avehicle, an operator may adjust the gain (or other parameters) forvarious controlled valves within either valve assembly in order toadjust the sensitivity (or aggressiveness, and so on) of the steeringcontrol for either set of wheels. For example, an operator may adjustthe gain of various proportional control valves within a rear valveassembly in order to adjust the aggressiveness of the rear steering,during rear steering assist mode, for a given manual steering input.

Notably, adjustments to steering control sensitivity may not be possible(at least to the same degree) for systems with a direct mechanicalcontrol link between the steering input device and the various steeringcontrol devices. Further, in various of the embodiments describedherein, certain adjustments to the front and rear valve assemblies by anoperator may be utilized for the manual or rear steering assist modesbut may be disregarded during operation of the vehicle in the automatedsteering mode. In this way, an operator may implement customizedsteering control for the rear steering assist and manual modes, withoutdisturbing a predetermined configuration of the steering system for theautomated mode. For example, the gain for various proportional controlvalves in a particular valve assembly may be adjusted by an operator forrear steering assist mode in order to decrease (or increase) the amountof steering at the rear wheels for a given manual steering input. Whenthe vehicle is transitioned from the rear steering assist mode to theautomated steering mode, the valve gains may then be automatically resetto a default (or other) setting to ensure appropriate automated control.Likewise, the gain for various proportional control valves in aparticular valve assembly may be automatically changed to a customizedsetting (e.g., to settings previously chosen by an operator) when thevehicle is transitioned from the automated steering mode to the rearsteering assist mode.

The disclosed steering system (and method) may also facilitate, amongother things, faster and easier transitions between various steeringmodes. In certain embodiments, where no direct mechanical link isprovided between the rear valve assembly and the steering input device,it may be possible to switch relatively quickly from the manual mode tothe rear-steering assist mode or to the automated mode. For example,with a vehicle operating in manual steering mode, the rear steeringassist mode may be engaged (or disengaged) by utilizing (or ignoring) asteering input signal from a steering sensor, rather than by necessarilydisconnecting (or otherwise disregarding) a mechanical connection.Likewise, a vehicle may be transitioned from the manual steering mode(and the rear steering assist mode) into the automated steering mode byswitching from control of front and rear steering device based uponmanual steering input (and related signals from the steering sensor) tocontrol of the front and rear valve assemblies based upon a targetvehicle path. Where there is no relevant mechanical link to sever (ordisregard) this switch may be effected quickly and automatically by, forexample, simply changing the control strategy implemented by acontroller at the front and rear valve assemblies.

Notably, due to the improved sensitivity and control of the disclosedsteering system (and method), it may be possible to safely andeffectively operate a particular vehicle that is utilized such a system(or method) at significantly elevated speeds. For example, the enhancedcontrol provided through active control of rear steering, whether in theautomated mode or the rear steering assist mode, may allow a vehicle tosafely and effectively travel at relatively high speeds withoutsignificant deviation from a target path of travel.

It will be understood that eliminating a direct mechanical link betweena steering input device and a steering control device, steering controlvalve assembly, or other device or system may not require the completeabsence of mechanical components from the relevant systems orassemblies. For example, various hydraulic control valves may includemechanical components such as pistons, gates, tubing, and so on, andvarious other at least partially mechanical devices (e.g., double-actingpistons) may also usefully be included in steering control. In thislight, this disclosure contemplates eliminating mechanical links betweensteering input devices and other components of a steering control system(e.g., rear steering devices) in the sense of configuring these (andrelated) devices and components to exchange control information viaelectronic, hydraulic, or other primarily non-mechanical means ratherthan through primarily mechanical means such as gears, racks, mechanicallinkages, and so on. In this light, a rack-and-pinion assembly (orsimilar mechanical mechanism) for transmitting steering information froma steering wheel to an electrohydraulic valve assembly or hydraulicsteering device may be viewed as providing a mechanical link between thesteering wheel and the valve assembly. In contrast, a signal linebetween a sensor on a steering column and a controller or valve assemblymay not provide a mechanical link between the steering column and thecontroller or valve assembly, even if the signal line, controller orvalve assembly includes mechanical elements such as check-valves,mechanical relays, and so on.

Referring now to FIG. 1, an example agricultural vehicle 10 is depicted.It will be understood that the configuration of the vehicle 10 presentedin FIG. 1 is intended only as an example and that other configurationsin keeping with this disclosure may be possible. As depicted in FIG. 1,the vehicle 10 may be an agricultural windrower, with a header 12 forcutting and gathering crop material (e.g., a draper platform). Frontwheels 14 may be fixed in a forward-facing orientation (i.e., may notpivot with respect to the vehicle 10), and may be independently drivenby respective hydrostatic machines to steer the front of the vehicle 10.For example, a hydraulic drive circuit 16 for each of the front wheels14, respectively, may include two different hydraulic (or other)machines such as a hydraulic pump (not shown in FIG. 1) driven by anengine 36 of the vehicle 10, and a hydraulic motor (not shown in FIG. 1)driven by the hydraulic pump. The motor-pump pairings of the respectivedrive circuits 16 may accordingly be used, respectively, to drive theleft-side and right-side wheels 14 at independent (and, potentially,different) rotational speeds. In this way, although the front wheels 14may not pivot with respect to the vehicle 10, the front wheels 14 may besteered (and may steer the vehicle 10) based upon the difference inspeed between the left-side front wheel 14 and the right-side frontwheel 14 (e.g., as controlled by the left-side and right-side hydraulicdrive circuits 16, respectively). As discussed in greater detail below,a front steering device of various configurations (not shown in FIG. 1)may be utilized to control the relative speeds of the hydraulic motors,and thereby control steering of the front wheels 14.

Rear wheels 18 may also be steerable wheels, although the rear wheels 18may be configured differently from the front wheels 14. For example, therear wheels 18 may be mounted, respectively, on casters 20, which mayallow the wheels 18 to rotate independently of each other and of a fixedrear-wheel support 22. It will be understood that various otherconfigurations of the rear wheels 18 may be possible, and that thecontrol architectures contemplated by this disclosure may also beemployed with non-caster rear wheels, or other configurations.

In the configuration depicted, if the rear wheels 18 and the casters 20are allowed to rotate freely, they may generally track turns of thevehicle 10 as it is otherwise steered (e.g., as the motors providedifferent speeds to each of the front wheels 14), but without the rearwheels 18 providing any active steering for the vehicle 10. For example,as the front wheels 14 turn the vehicle 10 to the left in the manualsteering mode, the turning (and continued forward motion) of the vehicle10 may cause the rear casters 20 to pivot to the left and thereby toturn the rear wheels 18 to track the turn of the vehicle 10. In certaininstances, however, if the rear wheels 18 are not actively steered, therear wheels 18 may tend to become misaligned with the path of travel ofthe vehicle 10. For example, due to ground impacts or other events, thewheels 18 may sometimes rotate on the casters 20 such that the wheels 18drag on the ground, rather than rolling, or such that the wheels 18 tendto steer the rear of the vehicle 10 away from the intended path oftravel of the vehicle 10.

The vehicle 10 may also include a cab 24 from which an operator maycontrol the operation of the vehicle 10. A steering input device, suchas a steering wheel 26, may be included in the cab 24, such that anoperator may direct the steering of the vehicle 10 (in certain steeringmodes) by providing manual steering input. It will be understood thatother steering input devices (e.g., levers, joysticks, touch-screendevices, and so on) may additionally (or alternatively) be utilized.Various other input devices may be also provided within the cab. Forexample, a hydraulic-system control device (e.g., a hydraulic controllever 32) may be provided for transitioning the vehicle between variousoperating modes (e.g., between an active operating mode in which varioushydraulic systems are operating, a parked mode in which the vehicle isin an energized state but various hydraulic systems may not beoperating, and so on).

Referring also to FIG. 2, an example configuration of the vehicle 10 isrepresented as an example vehicle 10 a. In order to control steering ofthe front or rear wheels 14 or 18 of the vehicle 10 a, a valve assembly40 may be integrated into a larger control circuit (as depicted in thevarious figures) such that the valve assembly 40 is in communicationwith various other components of the vehicle 10. The valve assembly 40may be in hydraulic communication with various components, such as rearsteering devices 42, and may be in electronic communication with variouscomponents, such as an electronic controller 58 (or other control unit).The valve assembly 40 may also be in communication (e.g., via amechanical connection) with components of the front hydraulic drivecircuit 16, such as hydraulic front drive pumps 16 a (or related controldevices such as control valves for the pumps 16 a, and so on). In thisway, for example, the valve assembly 40 may be utilized to control thespeed of the drive pumps 16 a (e.g., by mechanically adjusting the pumps16 a) in order to control, respectively, the speed of hydraulic frontdrive motors 16 b. Accordingly, because the front drive motors 16 b maybe driven independently, with respect to each other, the valve assembly40 may be utilized to control steering of the front wheels 14. The valveassembly 40 may also be utilized to control the rear steering devices 42(e.g., by hydraulically actuating the devices 42) in order to controlthe steering of the rear wheels 18.

In certain embodiments, the valve assembly 40 may include one or morehydraulic circuits, including various hydraulic valves (e.g.,electronically controlled valves) and various hydraulic and electricallines (see, e.g., FIG. 5). The valve assembly 40 may receive chargepressure and operating pressure from various pumps (e.g., pumps 44 and46) and may discharge pressure to one or more tanks (not shown in FIG.2). In certain embodiments, as discussed in greater detail below, thepump 44 may be configured as a lower pressure charge pump, and the pump46 may be configured as a higher pressure steering pump.

Control signals (e.g., hydraulic or electronic signals) may be receivedat the valve assembly 40 from a variety of sources, including thosespecifically discussed herein and various others. In certainembodiments, the controller 58 may be in electrical (or other)communication with various valves (or other components) of the valveassembly 40 in order to control the operation of those valves (or othercomponents). For example, various valves included in the valve assembly40 may be configured to operate based upon electronic steering commands(e.g., various electronic signals) from the controller 58 (or anotherdevice). The controller 58 may also be in electrical (or other)communication with a steering sensor 30 (connection to the controller 58not shown), various control circuits, various other electrohydraulicvalve assemblies (as shown, for example, in FIGS. 3 and 4), and so on.The controller 58 may be configured as a computing device with one ormore processors and memory architectures, as a hard-wired computingcircuit (or circuits), as a hydraulic or electrohydraulic controldevice, and so on.

It will be understood that the various control (and other) linesdepicted in the various figures may be viewed as representing, invarious configurations, either one flow line (or other signal line) ormultiple such lines. As such, unless specifically noted for a particularexample or implementation, it will be understood that the depicted linesmay be utilized to carry any variety of signals (e.g., hydraulic andelectrical signals), as may be appropriate. As such, for example, aparticular control line depicted in the various figures may, in certainimplementations, represent two or more control lines (e.g., anelectrical signal line and a hydraulic flow line). Further, it will beunderstood that lines (or other signal-transmission devices) may berouted between, and may connect to, various depicted (and hidden)components and assemblies in a variety of known ways. In certainembodiments, wireless transmission of electrical control signals may beutilized in place of wired connections.

In order to control the steering of vehicle 10 a based upon manualsteering input at the steering wheel 26, various hydraulic, electrical,or other components may be configured to provide signals (e.g.,hydraulic or electrical signals) to the valve assembly 40 (and variousother devices). In certain embodiments, for example, a manual steeringvalve 28 may be in communication with the steering wheel 26 such that anoperator turning the wheel 26 (i.e., providing a manual steering input)causes the valve 28 to provide a corresponding flow of hydraulic fluidto the valve assembly 40 (e.g., to a steering device included in thevalve assembly 40). In this way, manual steering input at the steeringwheel 26 may be implemented as hydraulic steering signals to steer thewheels of the vehicle 10 a. In certain embodiments, the valve 28 mayalternatively (or additionally) provide the hydraulic flow to otherdevices or assemblies (e.g., a steering device not included in the valveassembly 40, as depicted in the embodiment of FIG. 4).

In certain embodiments, the steering sensor 30 (e.g., an electronic orelectrohydraulic sensor) may also detect a manual steering input, suchas the turning of the wheel 26 (e.g., by detecting a rate of turning ofthe wheel 26 in a particular direction). The steering sensor 30 may thenprovide a corresponding steering input signal (e.g., an electronic orhydraulic signal) to the valve assembly 40, the controller 58 (signalline not shown), or various other devices, to facilitate steeringcontrol based upon the manual steering input. In certain embodiments,the sensor 30 may be an optical sensor that detects rotation of asteering column associated with steering wheel 26 and provides anelectrical signal representing the rotation of the steering column (and,thereby, of the steering wheel 26) to controller 58, or to one or morecontrol valves (or other devices or components) within electrohydraulicvalve assembly 40. In certain embodiments, other sensor types may beused, including Hall effect sensors, or others.

As noted above, it may sometimes be useful to control steering of thevehicle 10 a by actively steering the rear wheels 18 (e.g., in the rearsteering assist mode or the automated steering mode) as well as thefront wheels 14. As such, the vehicle 10 a may include various rearsteering devices, such as the hydraulically (or otherwise) operated rearsteering devices 42, which may be utilized to selectively control theorientation of the wheels 18 (or the casters 20). The steering devices42 may be controlled based upon hydraulic signals from the valveassembly 40, which may in turn be determined based upon various factors(e.g., manual steering input, as discussed above, or a target path oftravel, as discussed below). In certain embodiments, the rear steeringdevices 42 may be included as part of the valve assembly 40, rather thanas distinct components of the vehicle 10 a.

In certain embodiments, the steering devices 42 may be viewed as beingincluded in a dual-path hydraulic circuit (or system), such thatselectively routing hydraulic flow along a particular path of thedual-path circuit may result in the turning of one or both of the rearwheels 18 in a particular direction. For example, each rear steeringdevice 42 may include a double-acting hydraulic piston (not depicted inFIG. 2) that is connected to a pivot arm. The pivot arm, in turn, may beconnected to the corresponding caster 20 for the respective rear wheel18. In this way, through the actuation of the double-acting pistons, therear wheels 18 may be selectively (and independently) rotated in eitherdirection on the casters 20, in order to (independently) control thesteering of the rear wheels 18.

In certain embodiments, a particular pump (e.g., the pump 46) may beprovided for operation only of one (or both) of the rear steeringdevices 42 (and associated valve assemblies). In certain embodiments,the rear steering devices 42 (or various other devices and systemsdescribed herein) may share a pump (e.g., the pump 46, the pump 44, oranother pump (not shown in FIG. 2)) with one or more other devices orsystems. In certain embodiments, the pump 46 may be a high pressure pump(e.g., a high pressure “steering” pump) that may be configured to supplyhydraulic fluid for operation of the rear steering device 42 as well asvarious other devices. In certain embodiments, the pump 44 may be alower pressure charge pump that may be configured mainly to providecharge pressure to various hydraulic circuits or devices.

It will be understood, as also noted above, that various alternativeconfigurations may be possible. For example, the valve assembly 40 maydirectly include components such as the hydraulic motors 16 b, the pump44 (or various other pumps, such as the pump 46), the controller 58, andso on, or may communicate with such components via various signal linesexternal to the valve assembly 40. Similarly, as depicted in subsequentfigures, the valve assembly 40 may be replaced with (or separated into)multiple valve assemblies or other devices.

In certain embodiments, the valve assembly 40 (and related hydrauliccircuits) may not be disposed in hydraulic communication with thehydraulic drive circuits 16 (other than potentially draining to a sharedtank). For example, rather than hydraulic connections between the valveassembly 40 and the drive circuits 16, mechanical connections 34 may beprovided between a steering device of the valve assembly 40 and thepumps 16 a. As such, the speed of the pumps 16 a may be mechanicallycontrolled, based upon hydraulic steering signals from the valveassembly 40, hydraulic steering signals from the manual steering valve28, or other control signals. In contrast, no analogous mechanical linkmay be provided between the valve assembly 40 and the rear steeringdevices 42.

When the vehicle 10 a is operating in the manual steering mode, but notin the rear steering assist mode, the front wheels 14 may be steeredbased on the hydraulic flow through the manual steering valve 28. Forexample, manual steering input at the steering wheel 26 may regulatehydraulic flow through the manual steering valve 28. This hydraulicflow, in turn, as routed through via various intermediary devices, maycause the two pumps 16 a to drive the two front wheels 14 at differentspeeds. For example, a steering device (not shown in FIG. 2) included inthe valve assembly 40 may mechanically (or otherwise) adjust the speedof the pumps 16 a based upon hydraulic signals from the manual steeringvalve 28, in order to drive the front wheels 14, respectively, atappropriate speeds. In the manual steering mode, however, the valveassembly 40 may not actively control steering of the rear wheels 18 viathe rear steering devices 42. For example, no hydraulic flow may beprovided from the valve assembly 40 to the rear steering devices 42, andthe rear casters 20 may accordingly rotate relatively freely withrespect to the rear support 22.

In the rear steering assist mode, the front wheels may still be steeredbased on the hydraulic flow through the manual steering valve 28, asdiscussed above. The rear wheels 18, however, may be actively (andautomatically) steered based upon manual steering input at the steeringwheel 26. For example, the steering sensor 30 may detect a steering rate(or degree of steering) for a manual steering input received at thesteering wheel 26, and may provide a corresponding electronic signal tothe controller 58. The controller 58 may then provide a correspondingsteering command to the valve assembly 40, and thereby actuate the rearsteering devices 42 in order to hydraulically control the steering ofthe rear wheels 18. As noted above, the rear steering assist mode may beimplemented simultaneously with the manual steering mode.

In the automated steering mode, the rear wheels 18 may continue to besteered by the rear steering devices 42 based upon steering commandsprovided from the controller 58 to the valve assembly 40. In theautomated steering mode, however, such steering commands may not bebased upon any manual steering input at the steering wheel 26. Rather,the rear steering commands for the automated steering mode may beautomatically determined based upon a target path of travel for thevehicle 10 a. Similarly, in the automated steering mode, the frontwheels 14 may also be steered based upon steering commands provided fromthe controller 58 to the valve assembly 40, rather than manual steeringinput at the steering wheel 26. For example, a steering device (notshown in FIG. 2) included in the valve assembly 40 may adjust the speedof the pumps 16 a based upon steering commands provided from thecontroller 58 to the valve assembly 40, in order to drive the frontwheels 14, respectively, at appropriate speeds. In certain embodiments,detection of manual steering input at the steering wheel 26 (e.g.,detection by the steering sensor 30) may cause the vehicle 10 a to exitthe automated steering mode.

In certain embodiments, steering commands for the automated steeringmode (or other modes) may be determined based upon a target path oftravel for the vehicle 10 a. For example, a target path for the vehicle10 a (e.g., an “A to B” path across a field) may be determined invarious known ways. During operation, the current position of thevehicle 10 a may then be determined based upon location information froma GPS device 48 (or another location-detection system). Based uponvarious additional factors, such as the current speed or orientation ofthe wheels 14 or 18 or the current ground speed of the vehicle 10 a (asdetermined, for example, with various wheel speed sensors (not shown)),appropriate steering operations to maintain the desired path of travel(e.g., the target “A to B” path) may be determined, and correspondingsteering commands provided to the valve assembly 40 (or other devices)by the controller 58.

Referring also to FIG. 3, in a similar example configuration, designatedherein as vehicle 10 b, the functionality of the valve assembly 40 (seeFIG. 2) may be divided among two or more separate (but potentiallyinterconnected) valve assemblies, such as electrohydraulic valveassemblies 40 a and 40 b. In such a configuration, various functionalitymay be controlled by one or both of the separate valve assemblies 40 aand 40 b. For example, the valve assembly 40 b may be configured togenerally control automatic steering of the rear wheels 18 (e.g., in therear steering assist and automated steering modes), while the valveassembly 40 a may be configured to generally control automatic steeringof the front wheels 14 (e.g., in the automated steering mode). Incertain embodiments, a front steering device (not shown in FIG. 3) mayalso be included in the valve assembly 40 a, such that the valveassembly 40 a may also contribute to steering of the front wheels 14 inthe manual steering mode.

One or both of the valve assemblies 40 a and 40 b may be configured toreceive hydraulic flow from one or both of the pumps 44 and 46. Incertain embodiments, the pumps 44 and 46 may nonetheless operate onseparate hydraulic circuits (e.g., may not be in fluid communication,even if both pumps 44 and 46 are providing pressurized flow to one orboth of the valve assemblies 40 a and 40 b). For example, the pump 44may be configured as a charge pump providing pilot pressure to a firstportion of the valve assembly 40 b (e.g., to enable operation of thevalve assembly 40 b) as well as various other devices or systems (e.g.,for motor speed shifts or park brake release, to provide charge pressureto the drive pumps 16 a or power take-off drive pumps (not shown), andso on). In contrast, the pump 46 may be a higher pressure pump providingoperating pressure to a second portion of the valve assembly 40 b, whichmay be hydraulically isolated from the first portion.

In the configuration depicted in FIG. 3, hydraulic (or electrical)steering signals may be transmitted from the manual steering valve 28(or the steering sensor 30) to the valve assembly 40 a, or to variousother devices (e.g., the controller 58), based upon manual steeringinput at the steering wheel 26. Various other steering signals (e.g., anelectrical signal from the steering sensor 30 representing correspondingmanual steering input at the steering wheel 26) may also be transmittedto the controller 58, as well as to various other devices. As with theexample configuration depicted in FIG. 2, in the configuration of FIG.3, the valve assemblies 40 a and 40 b may also receive (and provide)electrical or hydraulic information from (and to) various othercomponents or systems of the vehicle 10 b, including those notspecifically depicted in the figures.

As with the configuration of FIG. 2, when the vehicle 10 b is operatingin the manual steering mode (but not also in the rear steering assistmode), the front wheels 14 may be steered based on the hydraulic flowthrough the manual steering valve 28, and the steering of the rearwheels 18 may not be actively controlled. For example, manual steeringinput at the steering wheel 26 may regulate hydraulic flow through themanual steering valve 28. This hydraulic flow, via various intermediarydevices, may then cause the two pumps 16 a to drive the two front wheels14 at different speeds. For example, a steering device (not shown inFIG. 3) included in the valve assembly 40 a may mechanically (orotherwise) adjust the speed of the pumps 16 a based upon hydraulicsignals from the manual steering valve 28, in order to drive the frontwheels 14, respectively, at appropriate speeds.

In the rear steering assist mode, the front wheels may still be steeredbased on the hydraulic flow through the manual steering valve 28, andthe rear wheels 18 may be automatically steered based upon electricalsignals from the steering sensor 30. For example, the steering sensor 30may detect a steering rate (or degree of steering) for a manual steeringinput received at the steering wheel 26, and may provide a correspondingelectrical signal to the controller 58. The controller 58 may thenprovide a corresponding steering command to the valve assembly 40 b, andthereby actuate the rear steering devices 42, in order to hydraulicallycontrol the steering of the rear wheels 18.

In the automated steering mode, the rear wheels 18 may be similarlysteered by the rear steering devices 42, based upon steering commandsprovided from the controller 58 to the valve assembly 40 b. In theautomated steering mode, however, such steering commands may be basedupon a target path of travel (e.g., a predetermined A-to-B path), ratherthan upon any manual steering input at the steering wheel 26. Indeed, incertain embodiments, detection of manual steering input at the steeringwheel 26 (e.g., detection by the steering sensor 30) may cause thevehicle 10 b to exit the automated steering mode.

When the vehicle 10 b is operating in the automated steering mode, thefront wheels 14 may also be steered based upon steering commandsprovided from the controller 58 to the valve assembly 40 a, rather thanany manual steering input at the steering wheel 26. For example, asteering device (not shown in FIG. 3) included in the valve assembly 40a may adjust the speed of the pumps 16 a based upon steering commandsprovided from the controller 58 to the valve assembly 40 a, in order todrive the front wheels 14, respectively, at appropriate speeds.

The controller 58 may control the valve assemblies 40 a and 40 b (orother devices or assemblies) in various ways. With regard to the valveassembly 40 a, for example, a steering command from the controller 58may be a current signal of appropriate intensity, which may be providedto a proportional valve (or valves) within the assembly 40 a (see, e.g.,FIG. 5). This may result in a particular flow of hydraulic fluid fromthe valve assembly 40 a to the relevant steering device, such that thefront wheels 14 are driven at appropriate (e.g., different) speeds.Similarly, a steering command from the controller 58 to the valveassembly 40 b may be another current signal of appropriate intensity,which may be provided to another proportional valve (or valves) withinthe assembly 40 b (see, e.g., FIG. 5). This may result in a particularflow of hydraulic fluid from the valve assembly 40 b to the rearsteering devices 42, such that the casters 20 (and, thereby, the rearwheels 18) are pivoted by an appropriate amount.

Referring also to FIG. 4, in certain embodiments, another examplevehicle 10 c may include a front hydraulic steering device 52 forcontrol of the steering of the front wheels 14, with the steering device52 being disposed separately from the valve assembly 40 a. The steeringdevice 52 may take a variety of forms, may receive electrical orhydraulic input from the steering valve 28, the valve assembly 40 a, orother devices, and may, in certain embodiments, be included in one orboth of valve assemblies 40 a and 40 b, rather than being configured asa separate component or device (e.g., as depicted in FIGS. 2 and 3).

As also noted above, one or both of the valve assemblies 40 a and 40 bmay be configured to receive hydraulic flow from one or both of thepumps 44 and 46. In certain embodiments, the pumps 44 and 46 maynonetheless operate on separate hydraulic circuits (e.g., may not be influid communication, even if both pumps 44 and 46 are providingpressurized flow to one or both of the valve assemblies 40 a and 40 b).For example, the pump 44 may be configured as a charge pump providingpilot pressure to a first portion of the valve assembly 40 b (e.g., toenable operation of the valve assembly 40 b), whereas the pump 46 may bea higher pressure pump providing operating pressure to a second portionof the valve assembly 40 b, which may be hydraulically isolated from thefirst portion.

In certain embodiments, including as depicted in FIG. 4, front steeringcontrol may be implemented via a dual-path hydraulic system within whichthe front steering device 52 is included. For example, the steeringdevice 52 may include a double-acting piston 52 a disposed within acylinder. Hydraulic fluid may be routed along either of two paths topressurize, respectively, either side of the piston 52 a and therebymove the piston 52 a within the cylinder. Depending on the relativeposition of the piston 52 a, the piston 52 a may control the front drivepumps 16 a in order to cause the respective drive motors 16 b to drivethe front wheels 14, respectively, at appropriate speeds. For example,through the mechanical connections 34 a, the particular position of thepiston 52 a within the cylinder may place the respective pumps 16 a inparticular operating states and, accordingly, cause the respectivemotors 16 b to rotate at particular speeds.

As depicted, the steering device 52 may be configured to receivehydraulic (or other) signals from the manual steering valve 28, viahydraulic line 54, as well as steering input from valve assembly 40 a,via hydraulic line 56. Accordingly, in the manual steering mode (with orwithout rear steering assist), a manual steering input at the steeringwheel 26 may cause the manual steering valve 28 to port more hydraulicfluid through one path of the dual-path hydraulic system than the other,thereby pressurizing a particular side of the piston 52 a and moving thepiston 52 a within the cylinder of the steering device 52. This, inturn, may mechanically (or otherwise) cause the hydraulic motors 16 b torotate at particular speeds and thereby steer the front wheels 14 in aparticular direction.

In the automated steering mode, the controller 58 may provide steeringcommands to the valve assembly 40 a (e.g., based upon a target path oftravel, position information from the GPS device 48, and other factors),in order to cause the valve assembly 40 a to route more hydraulic fluidthrough one path of the dual-path hydraulic system, thereby pressurizinga particular side of the piston 52 a. Again, this may move the piston 52a within the cylinder of the steering device 42 in order to cause thehydraulic motors 16 b to rotate at particular speeds and thereby steerthe front wheels 14 in a particular direction. In the automated steeringmode, no flow may be ported through the manual steering valve 28, suchthat front steering in controlled by the controller 58 but not by anymanual steering input.

Notably, the use of steering systems as described herein (e.g., systemsthat equip a manual steering input device such as the steering wheel 26with a manual steering valve and a steering sensor in communication withthe hydraulic valve assembly 40, the controller 58, and so on), mayallow for control of the steering of the various depicted vehicles 10,10 a, 10 b, and 10 c without the need for a direct mechanical link(e.g., a rack and pinion device, mechanical linkage, or other mechanicalassembly) between the steering input device (e.g., the steering wheel26) and certain other devices. Accordingly, the vehicle 10 (and others)may be easily transitioned between various steering modes. For example,for rear steering assist mode, manual steering input at the steeringwheel 26 may be translated to an electronic signal by the steeringsensor 30 rather than relayed directly as a mechanical (or hydraulic)signal to the rear valve assembly 40 b and the rear steering devices 42.As such, the vehicle 10 c may be easily transitioned in and out of therear steering assist mode (or automated steering mode), by utilizing (ornot utilizing) the signal from the steering sensor 30.

For convenience, example implementations of the various steering modeswill be described below with respect to the configuration of the vehicle10 c, as depicted in FIG. 4. It will be understood, however, thatsimilar principles may be applied with regard to the configurations ofthe vehicle 10 a in FIG. 2 and the vehicle 10 b in FIG. 3, as well asvarious other configurations.

As also noted above, in the manual steering mode for the vehicle 10 c,the front wheels 14 may be steered based upon manual steering inputprovided by an operator at the steering wheel 26, which input (or asignal derived therefrom) may be routed to the steering control device52 in order to control steering of the front wheels 14. In certainembodiments, as also described above, this control may be effected byway of a dual-path hydraulic system including the double-acting piston52 a. For example, an operator may turn the steering wheel 26 a certainamount (or with a certain steering rate), or may otherwise provide amanual steering input, in order to indicate a desired steeringoperation. This turning of the steering wheel 26 may cause the manualsteering valve 28 to selectively port hydraulic flow from the pump 44,in order to control the articulation of the steering piston 52 a withinthe steering device 52. For example, based upon the degree (or rate) ofsteering at the steering wheel 26, the manual steering valve 28 maydirect particular fractions of the flow from the pump 44 to either sideof the piston 52 a. Accordingly, the piston 52 a may be moved within thecylinder of the steering device 42 to cause the hydraulic motors 16 b torotate the wheels 14 at different rates, and thereby steer the vehicle10 c in the direction indicated by the manual steering input. At aneutral orientation (e.g., a mid-point or “centered” orientation along apath of travel), the piston 52 a may impose a zero steer condition, suchthat powering the front wheels 14 tends to drive the vehicle 10 csubstantially forward or backward (e.g., straight forward or backward).Such a neutral orientation may also be referred to as a “re-centered” or“zero-steer” orientation.

In certain implementations, when the vehicle 10 c is operating in themanual steering mode, operation of the valve assembly 40 a to activelycontrol steering of the front wheels 14 could interfere with the controlof front steering based upon the manual steering input at the steeringwheel 26. Accordingly, when the vehicle 10 c is being operated in themanual steering mode, the controller 58 may disable the valve assembly40 a (or a portion thereof) with respect to the steering of the frontwheels 14 and thereby prevent the valve assembly 40 a from controllingthe steering device 52 (or otherwise controlling the steering of frontwheels 14). In certain embodiments, for example, the controller 58 maydetermine that an operator is attempting to steer vehicle 10 c manuallybased upon the steering sensor 30 detecting a manual steering input atthe steering wheel 26. The controller 58 may then activate a blockervalve (see, e.g., FIG. 5) or other device associated with the valveassembly 40 a, in order to prevent the valve assembly 40 a fromactuating piston 52 a. In this way, in the manual steering mode, controlof the steering of the front wheels 14 may depend primarily on manualsteering input at the steering wheel 26 (e.g., rather than automatedsteering commands to the valve assembly 40 a from the controller 58).

It will be understood that other implementations of the manual steeringmode may also be possible. In certain embodiments, for example, thesensor 30 may detect a steering rate at steering wheel 26 (i.e., basedon a manual steering input at the steering wheel 26) and may provide acorresponding electronic (or other) signal to control (directly orindirectly) steering of the front wheels 14. For example, the controller58 may be configured to control the steering device 42 via the valveassembly 40 a, based upon a steering rate sensed by the sensor 30 (i.e.,based upon manual steering input). Alternatively (or additionally), thecontroller 58 may be configured to directly control the speeds of thepumps 16 a based upon such a signal from the sensor 30. For example, thecontroller 58 may electronically control the speed of the pumps 16 abased upon a steering rate detected by the steering sensor 30.Similarly, in certain embodiments, the sensor 30 may provide a controlsignal directly to the pumps driving the hydraulic motors 16 b, or tovarious other devices, based on manual steering input to the steeringwheel 26.

In certain embodiments, while the vehicle 10 c is operating in themanual steering mode (with respect to the front wheels 14), the rearwheels 18 may be controlled automatically. For example, in the rearsteering assist mode, which may be implemented simultaneously with themanual steering mode, the steering of the rear wheels 18 may becontrolled automatically based upon manual steering input at thesteering wheel 26 (or another steering input device). However, no directmechanical link may be provided between the steering wheel 26 and therear steering devices 42. For example, the steering sensor 30 (oranother device) may detect the rate (or degree) of steering of thesteering wheel 26, based upon the manual steering input, and maytransmit signals representing this rate (or degree) to the controller58. The controller 58 may then transmit corresponding steering commandsto valve assembly 40 b in order to control the rear steering. In certainembodiments, the valve assembly 40 b may be utilized to control rearsteering in the rear steering assist mode even if the valve assembly 40a has been disabled from controlling the steering of front wheels 14(e.g., as described above).

In certain embodiments, as also noted above, the rear steering devices42 may be utilized to steer the rear wheels 18 in the rear steeringassist mode. For example, based upon steering commands from thecontroller 58, the valve assembly 40 b may selectively direct hydraulicfluid flow from the pump 46 (or another pump) to each of the rearsteering devices 42 in order to control the steering of each of the rearwheels 18, respectively. In certain embodiments, the same amount of flowmay be directed to each of the left- and right-side steering devices 42,in order to effect approximately equal steering at each of rear wheels18. In certain embodiments, different amounts of flow may be directed tothe right-side device 42 and the left-side device 42, either becausecalibration of the steering system indicates that different signals arerequired at each steering device 42 to effect the same amount ofsteering at each of the respective steering devices 42, or becausedifferent rates of steering are desired at each steering device 42.

In certain embodiments, the rear steering devices 42 may also beincluded in a dual-path hydraulic circuit and may also employ hydraulicpistons similar to piston 52 a to control steering of rear wheels 18.For example, a double-acting piston 42 a (see FIG. 5) may be providedfor each of the rear steering devices 42, with the pistons 42 aconfigured, respectively, to rotate the rear wheels 18 on the casters20. The valve assembly 40 b may provide (or provide for) different fluidpressures at either side of a double-acting piston 42 a within either(or both) of the rear steering devices 42, based upon the steeringcommand received from the controller 58 (or from another device). Inresponse to this pressure differential, each piston 42 a may accordinglymove within its respective cylinder, in order to mechanically turn theassociated rear wheel 18.

The rear steering assist mode may be useful in various instances,including during operation of the vehicle 10 c at elevated speeds (e.g.,speeds exceeding 15 mph or more). At relatively low speeds, for example,the torque delivered to the front wheels 14 by the hydraulic motors 16 bmay be relatively large. Accordingly, even if the casters 20 do notnaturally align the rear wheels 18 with the direction of travel of thevehicle 10 c, the vehicle 10 c may be capable of maintaining anappropriate path of travel by overpowering any resistance from themisalignment of the rear wheels 18. At higher speeds, however, thetorque delivered to the front wheels 14 may be somewhat lower and theeffect of misalignment of the rear wheels 18 may be somewhat moresignificant. Accordingly, it may be useful to actively align the rearwheels 18 with the path of travel of the vehicle 10 c (i.e., to operatein the rear steering assist mode), so that the rear wheels 18 do noturge the vehicle 10 c away from a desired path of travel.

In certain embodiments, one or more of the depicted double-actingpistons may alternatively be configured as a single-acting piston. Forexample, one or both of the pistons 42 a may alternatively be configuredas a single-acting piston controlled by the valve assembly 40 b, with avalve of various known configurations being provided to control make-upoil for the pistons 42 a.

It will be understood, however, that the rear steering assist mode maybe useful at various speeds of the vehicle 10 c, and need not beutilized solely when the vehicle 10 c is traveling at relatively at highspeeds. For example, active steering of the rear wheels 18 duringsteering of the front wheels 14 may decrease the turning radius of thevehicle 10 c as a whole, which may result in improved operation of thevehicle 10 c within a field, even at low speeds. As also describedbelow, active steering of the rear wheels 18 may also be useful duringautomated steering of the front wheels 14 (e.g., for operation of thevehicle 10 c in the automated steering mode during a harvestingoperation).

In certain embodiments, as noted above, the vehicle 10 c may also beconfigured to operate in an automated steering mode, in which thesteering of the front wheels 14 and of the rear wheels 18 may becontrolled automatically (i.e., not based upon manual steering input atthe steering wheel 26). For example, a target path of travel for thevehicle 10 c may be determined in various known ways. During operationof the vehicle 10, and based upon the target path of travel, the currentposition of the vehicle 10 c (e.g., as determined based uponmeasurements by a GPS device 48), and various other factors, thecontroller 58 may then determine appropriate steering commands for thevalve assembly 40 a, in order to automatically control steering of thefront wheels 14. Similarly, the controller may also provide steeringcommands to the valve assembly 40 b, in order to automatically controlsteering of the rear wheels 18.

In certain embodiments, the vehicle 10 c may be configured toautomatically exit the automated steering mode upon receipt of a manualsteering input from the operator. For example, if the vehicle 10 c isoperating in the automated steering mode and an operator neverthelessturns the steering wheel 26, this manual steering input may be detectedby the steering sensor 30. Based upon the detected input, the controller58 may cease providing active steering input to one or both of the valveassemblies 40 a and 40 b, and may, in certain implementations, activelydisable one or both of the valve assemblies 40 a and 40 b.

The target path of travel for the vehicle 10 c and appropriate automaticsteering commands based upon the target path may be determined invarious ways, based upon various factors. In certain embodiments, asnoted above, the GPS device 48 (or a similar device) may be utilized inorder to determine a target path of travel of the vehicle or tootherwise determine appropriate steering commands for the automatedsteering mode. For example, for a harvesting operation, a target path oftravel for the vehicle 10 c may extend in a relatively straight lineacross a field. As the vehicle 10 c travels along the field, positioninformation for the vehicle 10 c from the GPS device 48, as well asother information (e.g., vehicle ground speed) may be utilized (e.g., bythe controller 58) to determine whether the vehicle 10 c has deviated(or is likely to deviate) from the straight line path. If a deviation(or an expected deviation) of a particular amount or degree from thetarget path of travel is detected, the controller 58 may provideappropriate commands to the valve assemblies 40 a and 40 b tocorrectively steer the front 14 and rear 18 wheels, respectively, andreturn the vehicle 10 c to (or keep the vehicle 10 c on) the path.

It will be understood that other configurations may be possible. Forexample, in certain embodiments, various controllers within the valveassembly 40 a (or other valve assemblies) may receive locationinformation directly from the GPS device 48, or the GPS device 48 mayinclude a controller for providing appropriate GPS-based steeringcommands directly to the valve assemblies 40 a and 40 b. Similarly, incertain embodiments, the controller 58 (or another device) may includean integrated position tracker (e.g., an integrated GPS device) (notshown).

In certain embodiments, as noted above, because there is no directmechanical control link between the steering wheel 26 and any of thevalve assembly 40 a and the steering devices 42, a common controlarchitecture (e.g., the pump 44 and the steering device 52) may beutilized to control steering of the front wheels 14 in both the manualand the automated modes, without the need to disconnect (or disregard) amechanical link between the steering wheel 26 and various steeringdevices to transition between the modes. Likewise, the rear wheels 18may be controlled with the same devices in both the rear steering assistmode (in which steering of the rear wheels 18 is based upon manualsteering input) and the automated steering mode (in which the rearwheels 18 are steered independently of manual steering input).

In certain embodiments, steering adjustments may be made simultaneously(or near-simultaneously) at both the front wheels 14 and the rear wheels18, in order to implement effective steering control for the vehicle 10c. In certain embodiments, steering adjustments may be madecontinuously, or near-continuously, as vehicle 10 c drives over a field.

Referring also to FIG. 5, a more detailed schematic of an examplesteering system is depicted, including example configurations of thevalve assemblies 40 a and 40 b. It will be understood that theconfiguration presented in FIG. 5 represents only an exampleconfiguration for the disclosed steering system. For example,alternative systems contemplated by this disclosure may include variousvalve types and configurations other than those depicted in FIG. 5, inorder to implement the contemplated steering control. It will further beunderstood that various other components and systems (includingcomponents and systems not depicted in FIG. 5) may interoperate with oneor more portions of the system depicted in FIG. 5. For example, the pump46 may be utilized to control steering of the rear wheels 18 as well asto lift and move the header 12 of the vehicle 10 c.

In the embodiment depicted, the manual steering valve 28 is in hydrauliccommunication with the piston 52 a, such that control of hydraulic flowthrough the valve 28 may move the piston 52 a and thereby control thespeeds of the hydraulic pumps 16 a. The valve assembly 40 a is also inhydraulic communication with the piston 52 a, such that hydraulic flowthrough the valve assembly 40 a may also move the piston 52 a andthereby control the speeds of the hydraulic pumps 16 a. As discussed ingreater detail below, the system may be configured such that only one ofthe valve 28 and the valve assembly 40 a controls the piston 52 asimultaneously (e.g., depending on whether the vehicle 10 c is operatingin the manual steering mode of the automated steering mode).

To control the rear steering, the valve assembly 40 b is in hydrauliccommunication with the rear steering devices 42, each of which includesa double-acting piston 42 a. Each piston 42 a may be in mechanicalcommunication with the respective caster 20 or rear wheel 18 (not shownin FIG. 5), such that movement of each piston 42 a may steer theassociated rear wheel 18. In this way, hydraulic flow through the valveassembly 40 b (e.g., as controlled by the controller 58 based upon atarget path of travel or a manual steering input at the steering wheel26 (not shown in FIG. 5)) may be utilized to control steering of therear wheels 18.

As depicted in FIG. 5, the valve assemblies 40 a and 40 b may beconfigured similarly (i.e., may include similar valve types andinter-valve connections). For example, each valve assembly 40 a and 40 bmay include a pilot-operated blocker valve (e.g., blocker valves 66 aand 66 b, respectively, operated by pilot valves 68 a and 68 b), variousmain flow control valves (e.g., variably-positioned main spool valves 70a and 72 a, and variably-positioned main spool valves 70 b and 72 b,respectively), and various proportional control valves (e.g., pilotvalves 74 a and 76 a, and pilot valves 74 b and 76 b, respectively) tocontrol the main flow control valves. These and various other componentsof valve assemblies 40 a and 40 b may be in communication with thecontroller 58 via various signal lines (including lines not shown inFIG. 5), such that the controller 58 may be configured to controloperation of the valve assemblies 40 a and 40 b to control steering ofthe front 14 and rear 18 wheels, respectively. As depicted, for example,electrical (e.g., current) signals provided by the controller 58 to thepilot valves 74 a, 74 b, 76 a and 76 b may cause a proportional (orother) opening, respectively, of the spool valves 70 a, 70 b, 72 a, and72 b. Automatic steering of the front 14 and rear 18 wheels may then becontrolled based upon this control of the spool valves 70 a, 70 b, 72 a,and 72 b.

The blocker valves 66 a and 66 b may be configured, respectively, todisable the valve assemblies 40 a and 40 b based upon receipt of anappropriate command (e.g., from the controller 58). As such, the blockervalves 66 a and 66 b may control, respectively, whether valve assemblies40 a and 40 b are engaged in active control, respectively, of the frontand rear steering. As depicted, for example, the blocker valves 66 a and66 b control the flow of fluid from the pumps 44 and 46, respectively,to the main spool valves 70 a and 72 a and to the main spool valves 70 band 72 b. As such, when disposed in a closed configuration (e.g., in adefault state), the blocker valves 66 a and 66 b may starve the spoolvalves 70 a, 72 a, 70 b and 72 b of flow and thereby effectively disablesteering of the front 14 and rear 18 wheels by the valve assemblies 40 aand 40 b.

In the manual steering mode, for example, the blocker valve 66 a may beoperated to cut off flow from the pump 44 through the spool valves 70 aand 72 a. Accordingly, in the manual steering mode, the manual steeringvalve 28, but not the valve assembly 40 a, may be used to controlsteering of the front wheels 14 via the steering device 52. Similarly,when the vehicle is not operating in the automated or rear steeringassist modes, the blocker valve 66 b may be operated to cut off flowfrom the pump 46 through the spool valves 70 b and 72 b. Accordingly, noautomatic control of the rear steering may be provided. (In certainembodiments, the blocker valve 66 b may not be operated in this way,such that rear steering may still be controlled automatically via valveassembly 40 b. As noted above, for example, the various vehicles 10 maybe configured to operate simultaneously in both the manual steering modefor the front wheels 14 and the rear steering assist mode for the rearwheels 18.)

As depicted, the blocker valves 66 a and 66 b are operated by pilotvalves 68 a and 68 b, respectively, with the pilot valves 68 a and 68 bboth being operated by the pump 44. Similarly, the opening and closingof the main spool valves 70 a, 70 b, 72 a, and 72 b may be controlled,respectively, by the pilot valves 74 a, 74 b, 76 a and 76 b, with eachof the pilot valves 74 a through 76 b also being operated by the pump44. (It will be understood that other pump arrangements are alsopossible.) Through control of the main valves 70 a, 70 b, 72 a, and 72 b(e.g., as implemented through control of the pilot valves 74 a, 74 b, 76a, and 76 b), the total flow through the valve assemblies 40 a and 40 bmay be controlled, as well as the relative amount of hydraulic flowdirected to opposing sides of the various double-acting pistons 42 a and52 a. Accordingly, with appropriate calibration of valve gains for agiven steering command (e.g., for a given electrical current signal),steering commands provided to the various pilot valves 74 a, 74 b, 76 aand 76 b may result in particular fluid flow through the various mainvalves 70 a, 70 b, 72 a, and 72 b and thereby in particular actuation ofthe pistons 42 a and 52 a. As discussed in greater detail above, thismay result in the particular steering operations at the front 14 andrear 18 wheels.

Although the valve assemblies 40 a and 40 b are depicted as exhibitinggenerally the same arrangement of valves (i.e., of the various valves 66a through 76 b), the assemblies 40 a and 40 b need not always beconfigured identically. In certain embodiments, for example, largersized (or otherwise higher-capacity) valves may be utilized in the valveassembly 40 b than in the valve assembly 40 a. This may be appropriate,for example, in order to account for higher expected pressures and flowrates within the valve assembly 40 b, as supplied by the higher-pressurepump 46 (as opposed to the lower-pressure charge pump 44). Calibrationand adjustment of the various valves 66 a through 76 b may also varybetween the valve assemblies 40 a and 40 b. For example, as a defaultconfiguration or as a result of adjustment by an operator, differentproportional gains may be utilized for various of the different pilotvalves 68 a, 68 b, 74 a, 74 b, 76 a, and 76 b.

Other configurations may also be possible. As depicted, for example, theoutputs of each of the main spool valves 70 b and 72 b are combined intoshared flow lines 96 and 98, such that the valves 70 b and 72 bcollectively control both of the pistons 42 a. In other embodiments, oneor more valves (e.g., the valve 70 b) may be provided for control of oneof the pistons 42 a, and a different one or more valves (e.g., the valve72 b) may be provided for independent control of the other of thepistons 42 a.

Similarly, in certain embodiments, one or more of the various pilotvalves 74 a through 76 b (or others) may be eliminated, and one or moreof the main valves 70 a, 70 b, 72 a, and 72 b may be configured,correspondingly, to operate without a pilot. For example, one or more ofthe main valves 70 a, 70 b, 72 a, and 72 b may be configured as a3-position, 4-way valve (not shown) that is closed to flow in itsdefault position.

In the rear steering assist mode, as also noted above, the front wheels14 may be steered manually and the valve assembly 40 b may receivecontrol signals based upon the manual steering input in order to provideassistive steering of rear wheels 18. As such, in the rear steeringassist mode, the blocker valve 66 b may be operated to permit hydraulicflow to the spool valves 70 b and 72 b. The steering sensor 30 maydetect a particular rate (or degree) of steering at the steering wheel26 (e.g., as may result from a manual steering input at the steeringwheel 26). A corresponding control signal may then be provided to one ormore of the pilot valves 74 b and 76 b in order to control the flowthrough the spool valves 70 b and 72 b. For example, an electronicsignal may be provided by the controller 58, as determined based uponthe manual steering input detected by sensor 30. The flow through thespool valves 70 b and 72 b may then control the movement of the pistons42 a within the rear steering device 42, and thereby control thesteering of the rear wheels 18.

In the automated steering mode, in which the steering of the frontwheels 14 and of the rear wheels 18 is automatically controlled, each ofthe blocker valves 66 a and 66 b may be operated to allow flow,respectively, to the spool valves 70 a and 72 a and to the spool valves70 b and 72 b. As also noted above, this flow may be provided by thepump 44 for the valve assembly 40 a and by the pump 46 for the valveassembly 40 b. A target path for the vehicle 10 c may be determined, andthe controller 58 may use position information from the GPS device 48 todetermine the deviation (or expected deviation) of the vehicle 10 c fromthe target path. The controller 58 may then provide appropriate steeringcommands to the valve assemblies 40 a and 40 b (i.e., to the pilotvalves 74 a and 76 a and the pilot valves 74 b and 76 b, respectively)in order to automatically steer the front 14 and rear 18 wheels.

With appropriate calibration, such automatic steering of the front 14and rear 18 wheels may correct the deviation from, and otherwise causethe vehicle 10 c to generally track, the target path of travel. Forexample, the GPS device 48 may provide to the controller 58 signalsrepresenting a current location of the vehicle 10 c. The controller 58may compare this current vehicle location to the target path of travel,in light of the current vehicle ground speed, degree of steering (e.g.,the current orientation of the rear wheels 18 or the current speeds,respectively, of the two front wheels 14), and so on, in order todetermine whether the vehicle 10 c is deviating (or is expected todeviate) from the target path of travel. If a deviation is detected (oranticipated), an appropriate command may then be provided to one or moreof the pilot valves 74 a, 74 b, 76 a. and 76 b in the valve assemblies40 a and 40 b, in order to effect appropriate steering control via thecontrol valves 70 a, 70 b, 72 a, and 72 b and the steering pistons 52 aand 42 a.

It will be understood that various adjustments may be possible to thesystem depicted in FIG. 5 (as well as other contemplated steeringsystems). In certain embodiments, for example, it may be possible foroperators to adjust various parameters relating to the valve assemblies40 and 40 b, such as the sensitivity of a particular valve or the gainat a particular valve for a particular control signal. For example, anoperator may selectively adjust the gain on various of the proportionalpilot valves 74 a, 74 b, 76 a, and 76 b in order to control the relativeamounts of hydraulic flow through the main valves 70 a, 70 b, 72 a, and72 b (and thereby the degree of steering of the front 14 and rear 18wheels) for a given steering command at the pilot valves 74 a, 74 b, 76a, and 76 b.

In certain embodiments, adjustments made to the valve assemblies 40 aand 40 b with respect to a particular operating mode may not be appliedin another operating mode. For example, in order to customize thesteering of the rear wheels 18 of the vehicle 10 c for the rear steeringassist mode, an operator may adjust the gains of the pilot valves 74 band 76 b of the valve assembly 40 b. Such adjustment may be useful, forexample, to increase (or decrease) the amount of steering of the rearwheels 18 (as controlled by the valve assembly 40 b and the pistons 42a) for a given manual steering input at the steering wheel 26 (as sensedby the steering sensor 30) and thereby customize the rear steeringassistance to the preferences of the operator. In certain embodiments,when the vehicle 10 c transitions from the rear steering assist mode tothe automated steering mode, the gains of the pilot valves 74 b and 76 bmay be automatically returned to a predetermined level (or levels) inorder to ensure appropriate coordination of the automatic front and rearsteering.

As also noted above, in certain embodiments, the pump 44 may be a lowerpressure pump than pump 46. Further, the pump 44 may be included in ahydraulic circuit that is not in hydraulic communication with thehydraulic circuit of the pump 46 (other than, potentially, draining tothe same hydraulic tank). For example, the pump 44 may be a charge pumpgenerally providing charge pressure to a charge pressure circuit 84,whereas the pump 46 may be a steering pump generally providing operatingpressure to a steering pressure circuit 86. A charge pump, it will beunderstood, is generally used in hydraulic systems to ensure that aparticular hydraulic circuit or device remains appropriately chargedwith fluid during normal operation. In practice, a charge pump not onlykeeps a particular circuit appropriately charged with fluid, but mayalso pressurize the circuit to a particular charge pressure. Typically,however, a charge pump does not provide operating pressure to motors orother devices. Using of a charge pump (i.e., the pump 44) to operate thefront steering device 52, rather than using a separate, dedicated pump,may result in significant cost and space savings, as well as otherbenefits.

The hydraulic circuits 84 and 86 are indicated generally with bracketsin FIG. 5. It will be understood that these brackets are approximate,and that some portion of the charge circuit 84 may extend into the leftportion of FIG. 5. As depicted in FIG. 5, portions of the chargepressure circuit 84 that extend into the valve assembly 40 b aredepicted in darker relief than other flow lines of the valve assembly 40b. It can be seen, accordingly, that although pressure from the chargepump 44 may be utilized to operate the pilot valves 74 b and 76 b of thevalve assembly 40 b, the charge pressure circuit 84 is not in hydrauliccommunication with the steering pressure circuit 86. In this way,although the valve assembly 40 b may be partially controlled by flowfrom the charge pump 44, pressurized flow from the charge pump 44 is notdirectly used to move the pistons 42 a (and thereby steer the rearwheels 18). As also noted above, the charge pump 44 may also provideoperating and pilot pressure to the valve assembly 40 a in the automatedsteering mode, such that flow from the pump 44 is utilized to controlthe valve assembly 40 a and to move the piston 52 a. Similarly, thecharge pump 44 may also provide pressurized flow through the manualsteering valve 28 in the manual and rear steering assist modes, also inorder to move the piston 52 a.

Because a charge pressure circuit (e.g., the circuit 84) may generallybe configured to operate at lower pressures than other circuits (e.g.,the steering pressure circuit 86 or the hydraulic drive circuit 16), acharge pump (e.g., the pump 44) may generally be configured to supplylower pressure hydraulic fluid than other pumps (e.g., the pump 46 orthe pump 16 a). As such, for example, the pump 44 may be configured toprovide fluid at relatively low pressures (e.g., between approximately150 psi and 700 psi). In contrast, the pump 46 may be configured toprovide fluid at relatively high pressures (e.g., between approximately1200 and 3600 psi). This configuration of the pump 46 may beappropriate, for example, because the pump 46 may need to provide enoughpressure to directly adjust the orientation of the rear wheels 18through direct movement of pistons 42 a. During operation of the vehicle10 c, this mechanical adjustment of the rear wheels 18 may sometimesrequire significant force (e.g., to overcome the weight of the vehicle10 c, as well as various ruts or other obstacles on the ground).Accordingly, it may be appropriate to provide a higher pressure pump forthe pump 46. In contrast, the pump 44 may need to provide only enoughpressure to move piston 52 a, with the higher pressure drive pump 16 aproviding motive power for the wheels based on the position of thepiston 52 a.

In the embodiment depicted, the valve assembly 40 a may be fullyincluded in the charge pressure circuit 84, such that the various valvesof the valve assembly 40 a may be fed with charge pressure from the pump44 and may also be actively operated by the pressure from the pump 44.For example, in order to automatically control the steering of the frontwheels 14, the pilot valves 74 a and 76 a may be operated by hydraulicfluid from the pump 44 (and the charge circuit 84) in order to open orclose the spool valves 74 a and 76 a. (The pilot valve 68 a may also becharged and operated by flow from the pump 44.) Further, the spoolvalves 74 a and 76 a may themselves regulate flow from the pump 44 (andthe charge circuit 84) to the steering device 52, in order to direct thesteering of the front wheels 14. Again, the use of the lower pressurecharge circuit 84 to operate the valve 40 a, as well as to providecharge pressure thereto, may be possible because the piston 52 a may notdirectly move the front wheels 14, but rather may steer the front wheels14 by controlling the speed of the higher-pressure drive pumps 16 a.

Also as depicted, the charge pressure circuit 84 is configured such thatthe charge pressure pump 44 provides flow through the manual steeringvalve 28 during the manual steering mode. In this way, even if the valveassembly 40 a is not being utilized to control steering of the frontwheels 14, the pump 44 may still be utilized to move the piston 52 a andthereby control the speed of the front wheels 14. As noted above, thecharge pressure pump 44 is also utilized to operate the valve assembly40 a during the automated steering mode, and to provide operate thepilot valves 68 b, 74 b, and 76 b in the valve assembly 40 b during therear steering assist and automated steering modes.

In contrast to the valve assembly 40 a, in the embodiment depicted, thevalve assembly 40 b may be integrated into the steering pressure circuit86 as well as the charge pressure circuit 84. For example, the pump 44may provide charge pressure to the valve assembly 40 b, with flow fromthe pump 44 operating the various pilot valves 68 b, 74 b and 76 b. Thesteering device 42, however, may be operated with hydraulic flow fromthe pump 46 and the steering pressure circuit 86, as routed through thevarious pilot-operated valves 66 b, 70 b, and 72 b. As noted above, thepump 46 and the steering pressure circuit 86 may be generally configuredto operate at significantly greater pressures than the pump 44 and thecharge pressure circuit 84. This may be useful, for example, inovercoming the resistance of ground features (e.g., ruts, mounds, rocks,branches, and so on) to the pivoting of the wheels 18.

The use of a higher pressure device for the pump 46 than for the pump 44(e.g., utilizing a charge pump for the pump 44) may also be useful ifthe pump 46 is utilized to operate other systems of the vehicle 10 c.For example, a priority valve 78 may be provided between the pump 46 andthe valve assembly 40 b. The valve 78 may be configured to control therouting of flow from the pump 46 to the valve assembly 40 b as well asto various other systems (not shown). Where operation of the othersystems (e.g., a lift or float system for the header 12) may requiresignificant hydraulic pressures, use of a sufficiently high pressurepump for the pump 46 may thus facilitate simultaneous (or other)operation of rear steering control (via the valve assembly 40 b) and ofthe other system by the pump 46. Even if simultaneous operation is notnecessary, the use of a higher pressure pump for the pump 46 may allow asingle pump to actuate the pistons 42 a as well as devices of othervarious systems (not shown).

The configuration of the pump 44 as a charge pump, which may alsoprovide charge pressure to various other systems (not shown) of thevehicle 10 c, may also provide significant cost and space savings forthe vehicle 10 c. For example, where a charge pump is already utilizedfor other systems of the vehicle 10 c, the use of the charge pump tooperate the valve assembly 40 a and to operate the piston 52 a may allowautomatic front steering to be implemented without the need for anadditional pump.

In certain implementations, control of the steering of the vehicle 10 cmay be implemented as part of a multi-mode steering (“MMS”) method suchas MMS method 200. The MMS method 200 may be represented as variousinstruction sets and subroutines stored on a storage device forming partof (or otherwise coupled to) the controller 58, and may be executed byone or more processors and one or more memory architectures (e.g., asincluded in or associated with the controller 58). In certainimplementations, the MMS method 200 may be a stand-alone method. Incertain implementations, the MMS method 200 may operate as part of, orin conjunction with, one or more other methods or processes and/or mayinclude one or more other methods or processes. Likewise, in certainimplementations, the MMS method 200 may be represented and implementedby an entirely hardware-based configuration or as a hydraulically ormechanically operated control structure, in addition or as analternative to a configuration having the MMS method 200 as a set ofinstructions stored in a storage device (e.g., a storage device includedin or associated with the controller 58). For the following discussion,the MMS method 200 will be described for illustrative purposes. It willbe understood, however, that other implementations may be possible.

Referring also to FIG. 6, in order to control steering of the rearwheels of a vehicle, the MMS method 200 may include determining 202 arear steering command (e.g., with the controller 58). In the automatedsteering mode, the determined 202 rear steering command may beautomatically determined 220 based upon a target path of travel for thevehicle. For example, a controller may utilize GPS and other informationin order to determine whether a vehicle is deviating (or is expected todeviate) from a target path of travel and may automatically determine220 a rear steering command based on that deviation (or expecteddeviation). In the rear steering assist mode, the rear steering commandmay alternatively be determined 202 based upon detecting 222 a manualsteering input. For example, a steering sensor may detect 222 a manualsteering input at a steering input device and may transmit acorresponding signal to a controller. The controller may then determine202 a rear steering command based upon the detected 222 manual input.

Once determined 202, the steering command may be provided 204 to a rearvalve assembly. The rear valve assembly may then hydraulically control206 a rear steering device in order to steer one or more rear wheels.For example, a controller may provide 204 an electronic (e.g., current)signal to one or more pilot valves included in the rear valve assembly.The various pilot valves may be configured, in response to the provided204 signal, to control other valves in the rear valve assembly andthereby control the hydraulic flow through the rear valve assembly inorder to control rear steering. For example, the pilot valves mayoperate two variably-adjustable spool valves in order to selectivelyport hydraulic fluid to either side of two double-acting cylinders andthereby to steer two associated rear wheels.

In certain implementations, the automated steering mode may beterminated 208 based upon detecting 224 a manual steering input. Forexample, during the automated steering mode, rear steering may behydraulically controlled 206 at a rear steering device with steeringcommands that have been automatically determined 220 based upon a targetpath of travel for the vehicle. In the automated steering mode,accordingly, an operator may not need to provide any manual steeringinput at the relevant steering input device (e.g., a steering wheel).Indeed, in certain implementations, detecting 224 a manual steeringinput at a steering input device may be taken as an indicator that anoperator wishes to exit the automated steering mode and manual controlmay be reinstated accordingly. In certain implementations, this maycorrespond to a disabling 210 of a front steering valve, and thesteering 212 of the front wheels based upon manual steering input. Incertain implementations, the vehicle may be transitioned to the rearsteering assist mode, with manual steering control of the front wheelsand automatic steering control of the rear wheels.

Referring also to FIG. 7, in order to control steering of the frontwheels of a vehicle, the MMS method 200 may include determining 230 afront steering command. In the automated steering mode, the determined230 front steering command may be automatically determined 246 basedupon a target path of travel for the vehicle. For example, a controllermay utilize GPS and other information in order to determine whether avehicle is deviating (or is expected to deviate) from a target path oftravel and may automatically determine 246 a rear steering command basedon that deviation (or expected deviation). In the manual steering mode,the front steering command may alternatively be determined 230 basedupon receiving 248 a manual steering input. For example, a manualsteering input may be received 248 at a steering input device (e.g., asteering wheel), such that a steering valve in communication with thesteering input device provides different hydraulic steering commands(i.e., different porting of hydraulic flow) based upon the manualsteering input.

Once determined 230, the steering command may be provided 232 to a frontsteering device or to a front valve assembly in communication with thefront steering device. In this way, the front steering device may behydraulically controlled 234 in order to control the front steering. Forexample, in the automated steering mode, a steering command may bedetermined 246 by a controller based upon a target path. The controllermay then provide 232 an electronic (e.g., current) signal to one or morepilot valves included in the front valve assembly. The various pilotvalves may be configured, in response to the provided 232 signal, tocontrol other valves in the front valve assembly and thereby control thehydraulic flow through the front valve assembly in order to control rearsteering. For example, the pilot valves may operate twovariably-adjustable spool valves in order to selectively port hydraulicfluid to either side of a double-acting cylinder and thereby to causepumps for driving the front wheels to rotate at different speeds. In themanual mode, in contrast, actuation of a manual steering valve by asteering input device may cause the valve to provide 232 a hydraulicsignal directly to the front steering device in order to similarly steerthe front wheels.

In certain implementations, the automated steering mode may beterminated 236 based upon detecting 250 a manual steering input. Forexample, during the automated steering mode, front steering may behydraulically controlled 234 at a front steering device with steeringcommands that have been automatically determined 246 based upon a targetpath of travel for the vehicle. In the automated steering mode,accordingly, an operator may not need to provide any manual steeringinput at the relevant steering input device (e.g., a steering wheel).Indeed, in certain implementations, detecting 236 a manual steeringinput at a steering input device may be taken as an indicator that anoperator wishes to exit the automated steering mode and manual controlmay be reinstated accordingly. In certain implementations, this maycorrespond to a disabling 238 of a front steering valve, and thesteering 240 of the front wheels based upon manual steering input.

In certain embodiments, it may be useful to disable automatic steeringof the front 14 or rear 18 wheels if it is determined that a relevantcontrol valve has become stuck (or if another steering fault isdetected). Referring again to FIG. 5, for example, if a valve within thevalve assembly 40 b (e.g., one or both of the main spool valves 70 b and72 b) becomes stuck (or otherwise malfunctions), hydraulic pressure atthe rear steering device 42 may tend to lock the rear wheels 18 in aparticular orientation. This may result in poor tracking by the rearwheels 18 of the steering executed at the front wheels 14, and inundesirable drag on the vehicle 10 c (e.g., if the rear wheels 18 arelocked by a stuck valve at an inappropriate angle, with respect to thedirection of travel of the vehicle 10 c).

In certain embodiments, in order to determine whether a valve within thevalve assembly 40 b has become stuck (or is otherwise malfunctioning), apressure sensor (e.g., the pressure sensor 92) may be included in (orotherwise placed in hydraulic communication with) the valve assembly 40b (or another valve assembly). If a stuck valve (or other detrimentalcondition) is detected, based upon pressure readings from such apressure sensor, rear steering control by the valve 40 b may beselectively disabled.

As depicted, the pressure sensor 92 is disposed in hydrauliccommunication with certain outlet lines 94 of both of the main spoolvalves 70 b and 72 b of the valve assembly 40 b. Due to theconfiguration of the valves 70 b and 72 b, these outlet lines 94 may bein hydraulic communication with the outlet lines 96 leading from thevalves 70 b and 72 b to the steering devices 42 when the valves 70 b and72 b are being utilized to control the steering devices 42. Accordingly,the pressure sensor 92 may be configured to detect an outlet pressurefor either of the valves 70 b and 72 b that may correspond to a controlpressure provided by the valve assembly 40 b to the steering devices 42(i.e., a control pressure within either of the outlet lines 96). Asdepicted, the pressure sensor 92 is in communication with both of thevalves 70 b and 72 b, such that the pressure sensor 92 is configured todetect the higher of the outlet pressures, respectively, of the twovalves 70 b and 72 b. Other configurations may also be possible.

If the pressure measured by the pressure sensor 92 does not match theexpected pressure for a particular steering command (e.g., a command bythe controller 58 to the pilot valves 74 b and 76 b for actuation of thespool valves 70 b and 72 b), it may be determined that one (or both) ofthe spool valves 70 b and 72 b have malfunctioned (e.g., are stuck).Accordingly, the controller 58 may cause the blocker valve 66 b to cutoff hydraulic flow to the valve assembly 40 b and thereby disable thevalve assembly 40 b from controlling the steering of the rear wheels 18.Similarly, if a pressure measured by the pressure sensor 92 does notmatch the expected pressure in the absence of a particular steeringcommand, it may be determined that one (or both) of the spool valves 70b and 72 b have malfunctioned (e.g., are stuck). Accordingly, thecontroller 58 may again cause the blocker valve 66 b to cut offhydraulic flow to the valve assembly 40 b and thereby disable the valveassembly 40 b from controlling the steering of the rear wheels 18.

Various control strategies may be implemented using the pressure sensor92 in order to address various potential issues with the valve assembly40 b. In certain implementations, as also noted above, the pressuresensor 92 may be utilized to monitor the outlet pressures of the mainvalves 70 b and 72 b. Upon detection of a particular pressure by thesensor 92, and based upon various other factors, including the speed ofthe vehicle 10 c, the nature of the present (or previous) steeringcommands provided to the valve assembly 40 b (or individual valvesthereof), and so on, the blocker valve 66 b may then be operated todisable the valve assembly 40 b. For example, if the vehicle 10 istraveling at a rate exceeding a threshold speed, and no steering commandis being presently provided to the valve assembly 40 b, a malfunction ofthe valve assembly 40 b may be identified based upon the pressure sensor92 detecting a pressure that is greater than a particular thresholdpressure. Similarly, if the vehicle 10 is traveling above a thresholdspeed, and a steering command is presently being provided to the valveassembly 40 b, a malfunction of the valve assembly 40 b may beidentified based upon the pressure sensor 92 detecting a pressure thatfails to increase by a threshold amount (or otherwise appropriatelychange) within a particular time after the start of the steeringcommand.

In certain implementations, such a strategy may usefully disable thevalve assembly 40 b when a particular valve of the valve assembly 40 bis stuck, but may not disable the valve assembly 40 b based simply upontransient pressure signals. For example, as the vehicle 10 c travelsalong a field, impacts on the rear wheels 18 (e.g., from stones, logsand so on) may introduce transient pressure spikes (and otherfluctuations) into the valve assembly 40 b via the double-acting pistons42 a of the steering devices 42. Accordingly, the pressure measured atthe pressure sensor 92 may exhibit transient spikes (and otherfluctuations) that are not related to stuck valves within the valveassembly 40 b (or other malfunctioning of the valve assembly 40 b). Incertain implementations, by controlling the blocker valve 66 b basedupon pressure readings at the pressure sensor 92 only when the vehicleis traveling above a threshold speed, unwarranted disabling of valveassembly 40 b may be avoided. In certain implementations, a thresholdspeed of 15 miles per hour (or higher) may be utilized.

In certain implementations, control of the valve assembly 40 b basedupon pressure readings at the pressure sensor 92 (or similar control ofthe valve assembly 40 b or of another valve assembly) may be implementedas part of a steering fault detection (“SFD”) method such as SFD method300. The SFD method 300 may be represented as various instruction setsand subroutines stored on a storage device forming part of (or otherwisecoupled to) the controller 58, and may be executed by one or moreprocessors and one or more memory architectures (e.g., as included in orassociated with the controller 58). In certain implementations, the SFDmethod 300 may be a stand-alone method. In certain implementations, theSFD method 300 may operate as part of, or in conjunction with, one ormore other methods or processes and/or may include one or more othermethods or processes. Likewise, in certain implementations, the SFDmethod 300 may be represented and implemented by an entirelyhardware-based configuration or as a hydraulically or mechanicallyoperated control structure, in addition or as an alternative to aconfiguration having the SFD method 300 as a set of instructions storedin a storage device (e.g., a storage device included in or associatedwith the controller 58).

For the following discussion, the SFD method 300 will be described forillustrative purposes. It will be understood, however, that otherimplementations may be possible. Further, although certain examplesherein discuss implementing the method 300 with respect to the valveassembly 40 b and the controller 58, it will be understood that otherimplementations may utilize (and control) other devices.

Referring also to FIG. 8, in certain implementations the SFD method 300may include determining 302 a ground speed of the agricultural vehicle.For example, a wheel speed sensor (not shown), an engine speed sensor(not shown), the GPS device 48, or another device (or devices) may beutilized to determine the rate at which the vehicle is traveling overthe ground. In certain implementations, the SFD method 300 may proceedonly if the determined 302 ground speed exceeds a particular threshold(e.g., 15 mph or higher).

Other threshold determinations may also be made. In certainimplementations, for example, the method 300 may include determining 324whether a gear has been selected for operation of the vehicle. If nogear has been selected, the vehicle may not be actively traveling andthe method 300 may terminate without identifying a fault in the relevantvalve assembly. In certain implementations, the method 300 may includeidentifying 326 whether the vehicle is currently subject to any knownsteering or other faults (e.g., a rear steering fault previouslyidentified by the method 300 or a steering fault in the relevantpressure sensor (e.g., the sensor 92). If an ongoing fault is identified326, the method 300 may also terminate (e.g., because the relevantcontrol systems may have already been disabled, in light of theidentified 326 ongoing fault).

If appropriate threshold determinations are satisfied (e.g., if anappropriate ground speed is determined 302, the vehicle is determined324 to be in gear, and no other ongoing faults are identified 326),method 300 may include determining 304 whether a steering command iscurrently being provided to the valve assembly 40 b. For example, withrespect to the vehicle 10 c, the controller 58 may determine 304 whetherthe controller 58 is currently providing a steering command to the pilotvalves 74 b and 76 b, in order to control steering of the rear wheels18. If a steering command is not determined 304 to be currently providedto the relevant valve assembly (e.g., the valve assembly 40 b), themethod 300 may terminate and without identifying a fault in the valveassembly.

The method 300 may also include determining 306 an operational pressureat the valve assembly 40 b. As depicted, the operational pressure may bedetermined 306 by the pressure sensor 92 and may indicate the greater ofthe output pressures, respectively, of the main valves 70 b and 72 b.Other arrangements may be possible.

If an appropriate ground speed is determined 302 (or other thresholddeterminations are met), and it is determined 304 that a steeringcommand is currently being provided, the method 300 may includedetermining 306 an operational (e.g., current) pressure at the relevantvalve assembly. In certain implementations, a pressure sensor 314 may beutilized to determine 306 the pressure of one or more hydraulic signalsbeing provided by the valve assembly to a steering device. For example,the pressure sensor 92 (see FIG. 5) may be configured to determine 306the larger of the output pressures of the valves 70 b and 72 b forcontrol of the steering devices 42.

A threshold pressure may be determined 308, based upon one or more ofthe determined 302 ground speed and the determination 304 of whether asteering command is being provided to the valve assembly 40 b. Thedetermined 308 threshold pressure may vary based on the determined 302ground speed, whether a steering command has been determined 304, andvarious other factors. For example, a larger pressure threshold (e.g.,between 1500 psi and 2300 psi) may be determined 308 if it is determined304 that no steering command is being provided and if the ground speedof the vehicle is determined 302 to be relatively high (e.g., 15 mph orhigher). A smaller pressure threshold may be determined 308, however, inother cases. (e.g., if it is determined 304 that a steering command iscurrently being provided).

In certain implementations, the pressure threshold may be determined 308based upon an expected change in operating pressure after implementationof a particular steering command. For example, where it has beendetermined 304 that a steering command is being provided to the relevantvalve assembly (e.g., the valve assembly 40 b), an initial pressure atthe valve assembly may be determined 320, for a time preceding the startof the determined 304 steering command. In certain implementations, forexample, the pressure sensor 92 may be configured to continuallydetermine 306 pressure data, such that the method 300 may includeinterrogating previously-recorded pressure measurements in order todetermine 320 an operating pressure immediately prior to the start of asteering command (i.e., an initial pressure). A particular offset (e.g.,as based upon the particular steering command, the determined 302vehicle speed, or other factors) may then be added 322 to the determined320 initial pressure in order to determine 308 the appropriate thresholdpressure.

With the threshold pressure and the pressure at the relevant valveassembly (or other device) having been determined 308 and 304, theoperational pressure at the valve assembly may be compared 310 to thethreshold pressure. Based upon this comparison 310, a steering fault maybe identified 312, and control of the rear hydraulic steering by therelevant valve assembly 40 b may be disabled 316, as appropriate. Forexample, if it has been determined 304 that no steering command iscurrently being provided, a steering fault (e.g., a stuck valve) may beidentified 312 based upon the operational pressure exceeding thedetermined 308 threshold pressure. Steering control by the valveassembly may then be automatically disabled 316. For example, in thevehicle 10 c, the blocker valve 66 b may be operated (e.g., viaelectronic control of the pilot valve 68 b) in order to disable 316 thevalve assembly 40 b.

Similarly, if it has been determined 304 that a steering command iscurrently being provided, a steering fault (e.g., a stuck valve) may beidentified 312 based upon the operational pressure failing to exceed thedetermined 308 threshold pressure within a particular amount of timeafter the steering command has been provided. For example, in thevehicle 10 c, if a steering command to the valve assembly 40 b does notresult in a particular pressure increase at the pressure sensor 92within a particular amount of time (e.g., 500 ms) of the steeringcommand being provided, the blocker valve 66 b may be operated todisable 316 the valve assembly 40 b.

Referring again to FIG. 5, when the vehicle 10 c (or 10 a or 10 b, andso on) is placed in a particular state, the various contemplatedsteering control systems may automatically return various steeringcomponents (e.g., pistons 42 a and 52 a of the steering devices 42 and52) to a default state. For example, upon detecting (in various knownways) that the vehicle 10 c is in a parked state, the valve assembly 40a may be controlled to automatically orient the piston 52 a within thecylinder of the steering device 52. In this way, when the vehicle 10 cis taken out of park it will be configured to initially travel in astraight, forward (or reverse) direction.

In certain implementations, for example, upon detecting that the vehicle10 c has been placed in park, the controller 58 may direct the valveassembly 40 a to automatically re-center the piston 52 a within thecylinder of the steering device 52. This re-centering of the piston 52 amay also, for example, usefully place the drive pumps 16 a in a neutralstate, such that the pumps 16 a cannot over-run the parking brake.

As also noted above, such an orientation of the piston 52 a (or anothera steering device or component thereof) may be viewed as a neutral,zero-steer, or “re-centered” state orientation. It will be understoodthat certain steering devices, including the piston 52 a, may be in aneutral or zero-steer state even if not oriented precisely at the centerof a relevant range of motion (i.e., even if not fully “centered”). Assuch, it will be understood that a “re-centered” state, may simply referto the zero-steer or neutral orientation of a steering device (e.g., thepiston 52 a), rather than necessarily indicating a physically centeredlocation of the steering device itself. Likewise, it will be understoodthat a small amount of steering (e.g., steering of a degree or so) maysometimes occur, even in a zero-steer state,

In the examples discussed below, re-centering of steering devices forthe front wheels 14 may be discussed in detail. It will be understoodthat, in certain embodiments, various adjustments to the rear wheels 18(e.g., via the rear steering devices 42) may also be made based upondetecting a particular vehicle state. For example, the valve assembly 40b may operate to re-center the rear pistons 42 a of the steering devices42, such that when the vehicle 10 c is taken out of park the rear wheels18 may be disposed for straight, forward (or reverse) travel.Alternatively, in certain embodiments, the valve 40 a (or the valve 40b) may simply be turned off (e.g., through actuation of the blockervalves 66 a or 66 b) upon detection of a particular vehicle state (e.g.,upon detecting that the vehicle 10 c has been placed in park). Incertain embodiments, position sensors (not shown) may be provided forthe pistons 42 a, the rear wheels 18, or other components, which sensorsmay be configured to detect the orientation of the rear wheels 18 suchthat the rear wheels 18 may be appropriately re-centered.

As noted above, it may be useful to re-center a steering system (i.e.,to dispose the system such that no steering of the relevant wheels iseffected) for various reasons. Re-centering steering for hydraulicallydriven wheels may, for example, assist in ensuring that steeringcommands do not cause the wheels to over-run a park brake. Re-centeringmay also help to ensure that excessive hydraulic (or other) pressure isnot stored within a steering (or drive) system, such that the relevantvehicle does not move unexpectedly when removed from park. In certainimplementations, the steering of the vehicle 10 c (or other similarvehicles) may be re-centered through a Steering Re-centering (“SR”)method, such as SR method 400.

Referring also to FIG. 9, the SR method 400 may include determining 402whether the agricultural vehicle is in a parked state. In certainimplementations, whether the vehicle is in a parked state may bedetermined 402 based upon sensors associated with hydraulic (or other)control devices for the vehicle. For example, determining 402 whether avehicle is parked may include determining 404 whether a control handle(e.g., a lever, dial, or knob), or other control device for control ofvehicle movement (e.g., a button, set of buttons, graphical userinterface, and so on) is disposed within a “neutral” range, at which noforward or rearward movement is commanded. With respect to the vehicle10 c, for example, the hydraulic control lever 32 (see FIG. 1) may beconfigured to be moved forward for forward drive and rearward forreverse drive. At a range of orientations between various forward andrearward positions, the control lever 32 may be treated as being inneutral (i.e., as commanding neither forward nor rearward travel). Whenthe vehicle 10 c is in a parked state, the drive system for vehicle 10 cis also typically in neutral. Accordingly, it may be useful to determine402 a parked state of the vehicle 10 c based upon determining 404 theorientation of the control lever 32.

Whether a vehicle is in a parked state may also be determined 402 basedupon determining 406 whether a park switch has been activated. Incertain implementations, a park switch may be a mechanical switch,configured to be activated (e.g., triggered) by movement of a controlhandle. In the vehicle 10 c, for example, a mechanical switch 32 a (seeFIG. 1) may be disposed such that the hydraulic control lever 32triggers (or releases) the switch 32 a when the control lever 32 issecured (at least somewhat) in neutral. This may have various effects,such as the automatic engagement of a park brake for the vehicle 10 c.Whether the vehicle 10 c is in a parked state may accordingly bedetermined 402 based upon, at least in part, determining 406 whether apark switch (e.g., the switch 32 a) has been activated by the lever 32.In other embodiments, a park switch may be configured to be activated bya feature other than a control handle (e.g., directly by manualmanipulation).

In certain implementations, the method 400 may include determining 402that a vehicle is in a parked state based upon determining 404 that acontrol handle of the vehicle has been in a neutral range for a firstpredetermined time interval 408. This may be useful, for example, toverify that the vehicle is actually in a parked state, before automaticre-centering of the relevant steering is commanded. For example, when anoperator uses the control lever 32 to transition the vehicle 10 c fromforward to reverse travel, the control lever 32 may be moved through theneutral range by the operator. In order to avoid commanding an automaticre-centering of the front wheels 14 in such a case (and others), it maybe useful to determine 402 a parked state of the vehicle 10 c only ifthe control lever 32 is determined 404 to be in its neutral range for aparticular timer interval 408 (e.g., 1.5 seconds or more).

In certain implementations, the method 400 may additionally (oralternatively) include determining 402 that a vehicle is in a parkedstate based upon determining 406 that a park switch has been activatedfor the first (or another) predetermined time interval 408. Again, thismay be useful to verify that the park switch has not been accidentally(and momentarily) activated and, accordingly, that the vehicle isactually in a parked state. For example, when the control lever 32passes through the neutral range it may tend to brush against orotherwise temporarily activate the park switch 32 a, even if no parkedstate is intended by the operator. In order to avoid an unwantedautomatic re-centering of the front wheels 14, it may accordingly beuseful to determine 402 a parked state of the vehicle 10 c only if thepark switch 32 a is determined 406 to have been activated for aparticular timer interval 408 (e.g., 1.5 seconds or more).

In certain implementations, it may be useful to implement automaticre-centering without the delay of the predetermined time interval 408(or other time intervals) for determining 404, 406 control handleorientation and park switch activation. For example, where a vehicle hasbeen de-rated (e.g., a maximum output of an engine, hydraulic pump, orother device adjusted downward), it may be useful to implement automaticre-centering promptly upon determining 402 any appropriate indicator ofa parked state. This may be appropriate, for example, because conditionsresulting in the de-rating of a vehicle (e.g., falling oil pressure,excessive coolant temperature, contradictory signals from relateddevices, such as a control lever and related park switch, and so on) maybe more likely to experience operational issues. As such, when a vehiclehas been de-rated and an appropriate re-centering trigger identified(e.g., activation of a park switch determined 406), it may be useful toautomatically re-center a steering system without significant delay(e.g., without waiting for the time interval 408).

Accordingly, in certain implementations, the method 400 may includedetermining 410 whether a vehicle is in a de-rated state. The method 400may then further include determining 402 that a vehicle is in a parkedstate (i.e., that automated re-centering of the wheels is appropriate)based upon determining 410 a de-rated state of the vehicle. In certainimplementations, the determination 410 of the de-rated state maydirectly prompt determination 402 of the parked state. For example, incertain embodiments, a steering system may be automatically re-centeredbased upon the determination 410 that the relevant vehicle has beende-rated (or has been de-rated in a particular way or with respect to aparticular system).

In certain implementations, if the vehicle is determined 410 to becurrently de-rated, the method 400 may include determining 402 that thevehicle is in a parked state based upon any number of additionalindicators, but without requiring a particular duration of time for theindicators. For example, where a vehicle has been determined 410 to havebeen de-rated, a parked state may be determined 402 immediately (i.e.,rather than after the time interval 408 noted above) based upon adetermination 404 of a neutral-range orientation of a control handle ora determination 406 of an activation of a park switch.

To further support re-centering of a steering system, the method 400 mayalso include determining 420 the present orientation of a relevantsteering device. For example, with respect to the vehicle 10 c, themethod 400 may include determining 420 the present orientation of thesteering piston 52 a. (It will be understood that for vehicles withdifferently configured steering devices, the orientation of otherfeatures may be determined.) The orientation of the piston 52 a may bedetermined 420 in various ways. In certain embodiments, for example, ananalog (or other) sensor such as a sensor 102 (see FIG. 5) may detectmovement of (or movement caused by) the piston 52 a. Signalscorresponding to this movement may then be converted (e.g., by thecontroller 58) into values representing the displacement of the piston52 a from a previously sensed position, the position of the piston 52 arelative to another reference orientation, or another indicator of theorientation of the piston 52 a.

The determined 420 present orientation of the steering device may thenbe compared 424 with a neutral orientation of the steering device (e.g.,a signal or value representing the present orientation subtracted from asignal or value representing the neutral orientation), in order todetermine whether the steering device is appropriately centered. Incertain implementations, as noted above, the neutral orientation of thesteering device may be a centered orientation of the steering device(e.g., as with the piston 52 a). It will be understood, however, thatother configurations are possible, such that re-centering a steeringsystem may not necessarily correspond to physical centering of arelevant steering device.

Based upon the comparison 424 of the present and neutral orientations ofthe steering device, the steering device may be moved 426 from thepresent orientation toward the neutral orientation. In certainembodiments, the steering device may be moved 426 based upon hydraulicflow through a relevant valve assembly, which flow may be controlled byvarious steering commands. With respect to the vehicle 10 c, forexample, the controller 58 may determine a target movement 426 of thepiston 52 a based upon the comparison 424 of the present and centeredorientations of the piston 52 a. Steering commands may then be providedby the controller 58 to various valves of the valve assembly 40 a, suchthat the resulting hydraulic flow through the valve assembly 40 a moves426 the piston 52 a towards its centered orientation.

In certain implementations, a range of orientations 422 of the steeringdevice around the neutral orientation (e.g., a range of distances of thepiston 52 a from its centered orientation) may be predetermined. Thisdetermined range 422 may serve, for example, to bound a dead-band gapfor control of the steering device, such that the device may not bemoved 426 (or may be moved 426 to a lesser degree) for re-centering whenthe device is determined 420 to be within the range 422. As such, incertain implementations, the method 200 may include determining a range422 of positions within a particular distance of a neutral position ofthe steering device (or a corresponding band-width of signals).Re-centering of the steering of the vehicle may then be implementeddifferently, depending on whether the steering device is determined 420to be presently oriented within the relevant range. For example, if thesteering device is determined 420 to be presently oriented within thepredetermined range 422 around the neutral orientation, but is notpresently at the neutral orientation, the steering device may beconsidered as almost being in its neutral orientation, such thatsubstantial additional movement 426 of the steering device may beunnecessary. Accordingly, the method 400 may include moving 426 thesteering device only for a predetermined time interval 428 (e.g., arelatively short time interval 428, such as 1 second). (It will beunderstood that the time interval 428 for providing 426 a steeringcommand may be different than, or may be the same as, the time interval408 to determine 404, 406 the state of a control handle or park switch.)

In contrast, if the steering device is determined 420 to be presentlyoriented outside of the predetermined range 422 around the neutralorientation, the steering device may appropriately be moved 426 (e.g.,through steering commands provided to the valve assembly 40 a) until thedetermined 420 present orientation is sufficiently close to the neutralorientation. For example, an initial set of commands to the valveassembly 40 a may cause the piston 52 a to move 426 over an extendedtime, until a sensor (e.g., sensor 102 in FIG. 5) indicates that thepiston 52 a is within a predetermined range 422 around the centeredorientation. A subsequent set of commands to the valve assembly 40 a maythen cause the piston 52 a to move 426 only for a limited, additional,predetermined time interval 428, before the steering commands areterminated. Such a strategy may, for example, cause the piston 52 a tobe moved 426 to within a close distance of its neutral position, withoutimposing substantial back and forth movement 426 around the neutralposition (e.g., as the control system “hunts” for neutral).

In certain embodiments, the relevant steering device may be moved bysuccessively smaller amounts 430 (or with successively smaller forces)as the steering device is determined to be approaching the neutralorientation. For example, as the piston 52 a is determined 420 to beapproaching its centered orientation, the controller 58 may providesuccessively smaller current signals to the various valves of the valveassembly 40 a, such that the piston 52 a is moved successively smalleramounts 430 by successively smaller hydraulic flows as the piston 52 anears center. This, and similar modulation of steering movements 426 mayresult in relatively smooth approach of the neutral orientation by thepiston 52 a (or another relevant steering device) and a less abrupt stopto the movement 426 of the steering device once an appropriately neutralorientation is reached.

In certain embodiments, various operations of the method 400 may beexecuted repeatedly in order to appropriately re-center a steeringsystem. For example, after the present orientation of a steering deviceis determined 420 and the steering device moved 426 accordingly, a newpresent orientation of the steering device may be determined 420 andcompared 424 with a neutral orientation in order to guide furthermovement 426 of the steering device.

In certain implementations, the method 400 may include stopping 444control of steering (e.g., stopping 444 the automatic moving 426 of asteering device) or turning off 444 an engine if an inversion ofsteering commands is detected (e.g., as may result if hydraulic linesare inadvertently misconnected). As such, the method 400 may includedetermining 440 a target direction of movement 426 of a steering device.A target direction of movement may be determined 440, for example, basedupon a steering command determined by a controller for the movement 426of the steering device. The determined 440 target direction of movementmay then be compared 442 to an actual direction of movement in order todetermine whether the actual direction of movement corresponds to thedetermined 440 target direction. With respect to the vehicle 10 c, forexample, the movement of the piston 52 a detected by the sensor 102 maybe compared to the target movement determined 440 by the controller 58.If the target and actual movements do not match (e.g., are in oppositedirections for at least a particular time interval), control of steeringmay be stopped 444 and the engine may be automatically turned off 444.

In certain implementations, the method 400 may also usefully guidemanual re-centering of various steering systems. This may be useful, forexample, if the engine of a vehicle is shut off (intentionally orotherwise) before an automatic re-centering of a steering system may becompleted. Accordingly, referring also to FIG. 10, the method 400 mayinclude determining 446 a shut-off condition for the engine of therelevant vehicle. An engine shut off may be determined 446 in variousknown ways, including via one or more sensors (not shown). The method400 may then include determining 448 whether a relevant steering devicehas been moved 426 to an orientation that is within an appropriate rangewith respect to the neutral orientation (e.g., moved 426 to withinparticular distance from the neutral orientation). In certainembodiments, this determined 448 range may include orientations of thesteering device that are disposed outside of the range 422.

If the steering device is determined 448 not to have been moved towithin the appropriate distance from the neutral orientation, thesteering device may be viewed as not being disposed at a neutral (i.e.,zero-steer) orientation. For various reasons, it may be useful toprevent a restart of the engine (and a corresponding powering of asteering drive) until the steering device is further moved, such thatthe engine may be restarted only if the steering system is in azero-steer state and any sudden movement of the vehicle upon enginerestart may be in a non-turning direction. Accordingly, upon identifying450 a restart input for restarting the engine (e.g., a turn of a key toa “run” position), the method 400 may include, before the engine isrestarted, providing 452 an indicator to an operator to guide a manualsteering input by the operator at the steering input device. Withrespect to the vehicle 10 c, for example, the controller 58 maydetermine 448 that the piston 52 a was not appropriately re-centeredbefore the engine of the vehicle 10 c was powered off. Upon theidentification 450 of a restart input for the vehicle 10 c (e.g., aturning of a relevant key to “run”), the actual restart of the enginemay be delayed until the steering system has been appropriatelyre-centered.

In certain implementations, the method 200 may determine 440 a targetdirection of movement for the piston 52 a (i.e., to re-center thesteering device 52) and may provide 452 an indicator directing theoperator to provide a particular manual input. For example, thecontroller 58 may provide 452 an indicator (e.g., an arrow or animatedsteering wheel) on a display device (not shown) in the vehicle 10 c,which may indicate which direction the operator should turn the steeringwheel 26. As the operator turns the steering wheel 26 (e.g., inaccordance with the provided 452 indicator), the present orientation ofthe steering device may be determined 420 and compared 424 with theneutral orientation. An updated indicator may then be provided 452 asappropriate for further manual steering. Once the steering device hasbeen determined 454 to have been moved to an orientation within a rangeof orientations around the neutral orientation, the steering device maybe viewed as appropriately re-centered and the engine 36 may berestarted 456. In certain embodiments, the acceptable range oforientations for a steering device may be larger for a manualre-centering (e.g., as guided by the provided 452 indicators) than for afully automated re-centering (e.g., as implemented via commands to thevalve assembly 40 a). For example, a steering device may be determinedto be appropriately re-centered, after a manual re-centering operation,if the steering device is determined 454 to be within a particular rangeof orientations, which may be a larger range than the range 422 forautomated re-centering of the steering device. This may, for example,allow for manual re-centering of a steering device, as guided byprovided 452 indicators, without requiring an operator to orient thesteering device with the same precision as in an automated re-centering.

Referring again to FIG. 5, in certain implementations, it may be usefulto provide an on-off or other valve to prevent hydraulic flow from themanual valve 28 from influencing an automated re-centering operation(e.g., a moving 426 of the piston 52 a based upon the various automateddeterminations 402, 404, 406, 410, 420, and so on). As depicted in FIG.5, an on-off valve 106 is disposed at the valve assembly 40 a in orderto selectively control operation of the valve 40 a (and other devices).In certain embodiments, a similar (or other) on-off valve (not shown)may be disposed at each of the flow lines 104 between the manualsteering valve 28 and the piston 52 a. When the piston 52 a is beingautomatically moved 426 during automated re-centering of the frontsteering system, the two valves (not shown) on the lines 104 may beturned off (or otherwise closed), such that no flow may be routed fromthe valve 28 to the piston 52 a.

As will be appreciated by one skilled in the art, certain aspects thedisclosed subject matter may be embodied as a method, system (e.g., awork vehicle control system included in the various vehicles 10), orcomputer program product. Accordingly, certain embodiments may beimplemented entirely as hardware, entirely as software (includingfirmware, resident software, micro-code, etc.) or as a combination ofsoftware and hardware (and other) aspects. Furthermore, certainembodiments may take the form of a computer program product on acomputer-usable storage medium having computer-usable program codeembodied in the medium.

Any suitable computer usable or computer readable medium may beutilized. The computer usable medium may be a computer readable signalmedium or a computer readable storage medium. A computer-usable, orcomputer-readable, storage medium (including a storage device associatedwith a computing device or client electronic device) may be, forexample, but is not limited to, an electronic, magnetic, optical,electromagnetic, infrared, or semiconductor system, apparatus, ordevice, or any suitable combination of the foregoing. More specificexamples (a non-exhaustive list) of the computer-readable medium wouldinclude the following: an electrical connection having one or morewires, a portable computer diskette, a hard disk, a random access memory(RAM), a read-only memory (ROM), an erasable programmable read-onlymemory (EPROM or Flash memory), an optical fiber, a portable compactdisc read-only memory (CD-ROM), an optical storage device. In thecontext of this document, a computer-usable, or computer-readable,storage medium may be any tangible medium that can contain, or store aprogram for use by or in connection with the instruction executionsystem, apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be non-transitory and may be anycomputer readable medium that is not a computer readable storage mediumand that can communicate, propagate, or transport a program for use byor in connection with an instruction execution system, apparatus, ordevice.

Aspects of certain embodiments are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of any flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in acomputer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablememory produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer implemented process such that theinstructions which execute on the computer or other programmableapparatus provide steps for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

The flowchart and block diagrams in the figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present disclosure. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The description of the present disclosure has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the disclosure in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of thedisclosure. Explicitly referenced embodiments herein were chosen anddescribed in order to best explain the principles of the disclosure andtheir practical application, and to enable others of ordinary skill inthe art to understand the disclosure and recognize many alternatives,modifications, and variations on the described example(s). Accordingly,various embodiments and implementations other than those explicitlydescribed are within the scope of the following claims.

What is claimed is:
 1. A steering system for an agricultural vehiclehaving one or more steerable front wheels, one or more steerable rearwheels, and a steering input device configured to receive a manualsteering input for the one or more steerable front wheels, the steeringsystem comprising: a rear hydraulic steering device coupled to at leastone of the one or more steerable rear wheels; a rear valve assemblyconfigured to control the rear hydraulic steering device in order tosteer the at least one steerable rear wheel; and a controller configuredto determine a rear steering command and provide the rear steeringcommand to the rear valve assembly; wherein the rear valve assemblycontrols the rear hydraulic steering device based upon, at least inpart, the rear steering command from the controller; wherein, in amanual steering mode, the controller does not determine a rear steeringcommand for the rear valve assembly such that the rear wheels are freelyrotatable; wherein, in a rear steering assist mode, the controllerdetermines the rear steering command based upon, at least in part, themanual steering input; and wherein, in an automated steering mode, thecontroller determines the rear steering command based upon, at least inpart, a target path of the agricultural vehicle that is determinedindependently of the manual steering input.
 2. The steering system ofclaim 1, further comprising: a steering sensor in communication with thesteering input device and the controller; wherein the steering sensor isconfigured to provide a steering input signal based upon, at least inpart, the steering sensor detecting the manual steering input receivedat the steering input device; and wherein, in the rear steering assistmode, the controller determines the rear steering command based upon, atleast in part, the steering input signal from the steering sensor. 3.The steering system of claim 1, wherein, in the automated steering mode,the controller determines the rear steering command independently of anymanual steering input received by the steering input device.
 4. Thesteering system of claim 3, wherein the automated steering mode isterminated based upon, at least in part, receiving the manual steeringinput at the steering input device.
 5. The steering system of claim 1,further comprising: a front hydraulic steering device coupled to atleast one of the one or more steerable front wheels; and a front valveassembly configured to control the front hydraulic steering device inorder to steer the at least one steerable front wheel based upon, atleast in part, a front steering command received by the front valveassembly from the controller; wherein, in the automated steering mode,the front valve assembly controls the front hydraulic steering device toautomatically steer the at least one steerable front wheel based upon,at least in part, the front steering command, the front steering commandbeing based upon, at least in part, the target path of the agriculturalvehicle; and wherein, in the rear steering assist mode, the fronthydraulic steering device steers the at least one steerable front wheelbased upon, at least in part, the manual steering input.
 6. The steeringsystem of claim 5, wherein the rear wheels are mounted to a rear-wheelsupport by casters to rotate independently of each other and therear-wheel support.
 7. The steering system of claim 1, wherein one ormore valves included in the rear valve assembly are adjustable in orderto adjust the control of the rear hydraulic steering device by the rearvalve assembly for a particular rear steering command from thecontroller and for a particular manual steering input at the steeringinput device; and wherein adjusting the control of the rear hydraulicsteering device by the rear valve assembly changes a degree of steeringof the at least one steerable rear wheel by the rear hydraulic steeringdevice for the particular rear steering command and for the particularmanual steering input.
 8. The steering system of claim 1, wherein therear hydraulic steering device includes a dual-path hydraulic system andwherein the steering of the at least one steerable rear wheel iscontrolled, at least in part, by the rear valve assembly controllinghydraulic flow to the dual-path hydraulic system.
 9. The steering systemof claim 8, wherein the rear hydraulic steering device is coupled tofirst and second steerable rear wheels, respectively, with first andsecond pistons of the dual-path hydraulic system; wherein the rear valveassembly controls steering of the first steerable rear wheel bycontrolling hydraulic flow to the first piston; and wherein the rearvalve assembly controls steering of the second steerable rear wheel bycontrolling hydraulic flow to the second piston.
 10. The steering systemof claim 1, wherein the rear valve assembly receives pressurizedhydraulic fluid from a pump; and wherein the rear valve assemblyincludes: first and second pilot valves configured to receive the rearsteering command from the controller; first and second main spool valvesarranged in parallel between the pump and the rear hydraulic steeringdevice, wherein the first and second main spool valves are controlled bythe first and second pilot valves, respectively; and a blocker valvedisposed between the pump and the first and second main spool valves,wherein the blocker valve is configured to block flow from the pump tothe first and second main spool valves in order to disable the rearvalve assembly.
 11. A steering method for an agricultural vehicle havingone or more steerable front wheels, one or more steerable rear wheels, asteering input device configured to receive a manual steering input forthe one or more steerable front wheels, a rear hydraulic steering devicecoupled to at least one of the one or more steerable rear wheels, a rearvalve assembly configured to control the rear hydraulic steering devicein order to steer the at least one steerable rear wheel, and acontroller, the steering method comprising: determining, in at least onemode, a rear steering command by a controller; providing, in at leastone mode, the rear steering command to the rear valve assembly; andcontrolling, in at least one mode, the rear hydraulic steering devicewith the rear valve assembly based upon, at least in part, the rearsteering command from the controller; wherein, in a manual steeringmode, the controller does not determine a rear steering command for therear valve assembly such that the rear wheels are freely rotatable;wherein, in a rear steering assist mode, the rear steering command isdetermined based upon, at least in part, the manual steering input; andwherein, in an automated steering mode, the rear steering command isdetermined based upon, at least in part, a target path of theagricultural vehicle that is determined independently of the manualsteering input.
 12. The steering method of claim 11, wherein theagricultural vehicle further includes a steering sensor in communicationwith the steering input device and the controller; and furthercomprising providing a steering input signal based upon, at least inpart, the steering sensor detecting the manual steering input receivedat the steering input device; wherein, in the rear steering assist mode,the rear steering command is determined based upon, at least in part,the steering input signal from the steering sensor.
 13. The steeringmethod of claim 11, wherein in the automated steering mode, the rearsteering command is determined independently of any manual steeringinput received by the steering input device.
 14. The steering method ofclaim 13, wherein the automated steering mode is terminated and the rearsteering assist mode is initiated based upon, at least in part,receiving the manual steering input at the steering input device. 15.The steering method of claim 11, wherein the agricultural vehiclefurther includes: a front hydraulic steering device coupled to at leastone of the one or more steerable front wheels; and a front valveassembly configured to control the front hydraulic steering device inorder to steer the at least one steerable front wheel based upon, atleast in part, a front steering command received by the front valveassembly from the controller; wherein, in the automated steering mode,the front valve assembly controls the front hydraulic steering device toautomatically steer the at least one steerable front wheel based upon,at least in part, the front steering command, the front steering commandbeing based upon, at least in part, the target path of the agriculturalvehicle; and wherein, in the rear steering assist mode, the fronthydraulic steering device steers the at least one steerable front wheelbased upon, at least in part, the manual steering input.
 16. Thesteering method of claim 11, wherein the rear wheels are mounted to arear-wheel support by casters to rotate independently of each other andthe rear-wheel support.
 17. The steering method of claim 11, wherein oneor more valves included in the rear valve assembly are adjustable inorder to adjust the control of the rear hydraulic steering device by therear valve assembly for a particular rear steering command from thecontroller and for a particular manual steering input at the steeringinput device; and wherein adjusting the control of the rear hydraulicsteering device by the rear valve assembly changes a degree of steeringof the at least one steerable rear wheel by the rear hydraulic steeringdevice for the particular rear steering command and for the particularmanual steering input.
 18. The steering method of claim 11, wherein therear hydraulic steering device includes a dual-path hydraulic system andwherein the steering of the at least one steerable rear wheel iscontrolled, at least in part, by the rear valve assembly controllinghydraulic flow to the dual-path hydraulic system.
 19. The steeringmethod of claim 18, wherein the rear hydraulic steering device iscoupled to first and second steerable rear wheels, respectively, withfirst and second double-acting pistons of the dual-path hydraulicsystem; wherein the rear valve assembly controls steering of the firststeerable rear wheel by controlling hydraulic flow to the firstdouble-acting piston; and wherein the rear valve assembly controlssteering of the second steerable rear wheel by controlling hydraulicflow to the second double-acting piston.
 20. The steering method ofclaim 11, wherein the rear valve assembly receives pressurized hydraulicfluid from a pump; and wherein the rear valve assembly includes: firstand second pilot valves configured to receive the rear steering commandfrom the controller; first and second main spool valves arranged inparallel between the pump and the rear hydraulic steering device,wherein the first and second main spool valves are controlled by thefirst and second pilot valves, respectively; and a blocker valvedisposed between the pump and the first and second main spool valves,wherein the blocker valve is configured to block flow from the pump tothe first and second main spool valves in order to disable the rearvalve assembly.